¶1At trial in the Superior Court, a jury found the Commonwealth liable under the Massachusetts Tort Claims Act, G. L. c. 258, § 2 (1986 ed.), for the negligent failure of Lawrence Tierney, a probation officer, to verify the place of employment of Edward Darragh, a probationer in Tierney’s charge. Darragh, a thrice-convicted child molester, was employed as a teacher in the Boston public schools in violation of the special conditions of his probation; during the term of his probation, Darragh sexually molested the plaintiffs, two of his students. The jury awarded A.L. and M.M. damages against the Commonwealth. The Commonwealth appeals. We granted the Commonwealth’s application for direct appellate review. We affirm.
¶2Edward Darragh was convicted on January 5, 1978, in the Waltham District Court on nine counts of indecent assault and battery on children under the age of fourteen and contributing to the delinquency of minors. Prior to this conviction, Darragh had been convicted twice in 1966 in the Malden and Woburn District Courts for indecent assault and battery on a child under the age of fourteen and for two counts of unnatural acts with young boys between the ages of ten and thirteen. For his 1978 conviction, Darragh received an eighteen-month suspended sentence. As specific conditions of his probation, the sentencing judge directed that Darragh (1) refrain from teaching; (2) refrain from associating with young boys; (3) continue psychotherapy during probation; and (4) sign any releases needed for dissemination of probation information.
¶3*237Supervision of Darragh’s probation was assigned to Probation Officer Lawrence Tierney. Tierney met with Darragh regularly, spoke with him periodically by telephone, and saw to it that Darragh consulted a competent psychiatrist. However, apart from noting Darragh’s own averments of employment as a salesman, Tierney made no attempt to verify Darragh’s employment.
¶4Contrary to Darragh’s representations, he was, in fact, teaching science at the Barnes Middle School in East Boston throughout the period of his probation. Between the fall of 1978 and his arrest in February, 1979, Darragh repeatedly molested M.M., then a sixth grade student. During January and February, 1979, Darragh sexually assaulted A.L., then thirteen years old. Darragh molested both boys in a locked storage room at the school and maintained secrecy by threatening to molest A.L.’s younger brother if A.L. told anyone of the assaults.
¶5Despite a complaint by the mother of another student who witnessed Darragh’s abusive behavior,
¶6A.L,, acting through his parents,
¶7The city of Boston settled with each plaintiff prior to trial.
¶8With these facts in mind, we address the issue whether the Commonwealth is liable for the probation officer’s negligent failure to ascertain Darragh’s place of employment. In so doing, we must determine (1) whether the probation officer owed a duty to the plaintiffs in this case, and (2) whether the Commonwealth is liable under the Massachusetts Tort Claims Act for the probation officer’s negligent violation of such a duty.
¶9*2391. The probation officer’s duty. “In order to recover against the [Commonwealth] for negligence [of the probation officer], the plaintiff must show (1) the existence of an act or omission in violation of a (2) duty owed to the plaintiffs by the defendant, (3) injury, and (4) a causal relationship between the breach of duty and the harm suffered.” Dinsky v. Framingham, 386 Mass. 801, 804 (1982). The parties properly focus their arguments on Dinskyand on Irwin v. Ware, 392 Mass. 745 (1985). We conclude that the trial judge correctly determined that, “given the potential harmful effects upon the class sought to be protected,” there was a duty owed to these plaintiffs, and that this case is closer to Irwinthan it is to Dinsky.
¶10In Dinsky, flooding damaged the plaintiffs’ house because the house was located on an improperly graded lot. Prior to construction, the town’s department of health had notified the building commissioner that the property should be graded “to prevent low spots that will not drain and create a public nuisance,” and instructed the building commissioner to inspect the lot before issuing a building permit. The building commissioner issued the permit without inspecting the property, which was, indeed, improperly graded. Dinsky, supra at 802. We held the town not liable for its failure to inspect the lot prior to issuing the building permit, because “the purpose of a building code has been considered traditionally to be the protection of the general public,” not protection of the property owner. Id. at 805. Thus, the building commissioner owed no special duty to the plaintiffs in Dinsky.
¶11*240In Irwin, we held a municipality liable for the failure of its police officers to remove an obviously intoxicated driver from the road after the police had stopped the driver for driving too fast. Ten minutes later, the driver was involved in an accident which resulted in the deaths of the plaintiff’s decedents. Irwin, supra at 764. We concluded that, where the negligent act of a public official threatens immediate and serious physical injury to an identifiable class, and the class has no chance to protect itself from the harm threatened, the official owes a duty of care to that class. Id. at 756. We noted, too, that the most critical factor in this analysis is whether a defendant could anticipate that he would be expected to act to protect the plaintiff and could foresee harm to the plaintiff resulting from his inaction. See id.
¶12In analyzing this case under the criteria set forth in Irwin, we first address the question whether Tierney owed a duty to *241these plaintiffs beyond the duty he owed to the general public. As we noted in Irwin, “[w]hile several different categories of such special relationships are recognized in the common law, they are based to a large extent on a uniform set of considerations. Foremost among these is whether a defendant reasonably could foresee that he would be expected to take affirmative action to protect the plaintiff and could anticipate harm to the plaintiff from the failure to do so. . . .It has been said that such foreseeability can be based on reasonable reliance by the plaintiff, impeding other persons who might seek to render aid, statutory duties, property ownership or some other basis.” (Citations omitted.) Id. at 756. We think that the conditions of probation imposed by the sentencing judge created a special relationship between these plaintiffs and the probation officer and created a duty beyond that owed to the public as a whole.
¶13It is clear that the sentencing judge’s conditions of probation were designed to protect young boys. The sentencing judge determined that Darragh would molest again if he entered an environment in which he was permitted frequent association with young boys.
¶14The Commonwealth asserts that, even if it was foreseeable that Darragh would molest young boys again, the probation officer owed no special duty to these plaintiffs. The Commonwealth argues that G. L. c. 276, § 85 (1986 ed.), which defines the duties of probation officers, creates a duty to the courts alone. We do not agree. The duties outlined in G. L. c. 276, § 85, clearly are not intended to be an exhaustive list of the duties of probation officers. Although the statute provides that probation officers “shall perform such . . . duties as the court *242requires,” this language does not exclude all other duties. Historically, the purpose of probation in Massachusetts has been to aid probationers in becoming law-abiding citizens. Indeed, Massachusetts was the first State to use probation and did so prior to any statutory enactment. Thus, in this Commonwealth, a probation officer’s duty never has been limited to service of the court alone. See Carter, Some Aspects of Massachusetts Probation Law and Practice, 42B.U.L. Rev. 32, 32-33, 38-39 (1962).
¶15The duties of each probation officer are defined and informed by the specific instructions of the sentencing judge. See ABA Standards Relating to the Administration of Criminal Justice §§ 3.1-3.2, at 398 (1974) (noting that conditions of probation appropriately deal with many matters designed to help probationer lead a law-abiding life, and that specific conditions of probation should not be required by statute, but by the sentencing judge’s instructions). Although it is the function of the sentencing judge to set the conditions of probation, the conditions are meaningless without the probation officer’s enforcement. See generally Carter, supra. Thus, Tierney’s duty was defined by the judge’s conditions of probation.
¶16The Commonwealth next contends Tierney owed no duty to the plaintiffs, because the events in this case followed a leisurely course. In mating this argument, the Commonwealth points out that the acts of molestation complained of took place nine months after Darragh’s sentencing. The Commonwealth asserts that the time frame involved in this case renders Irwin, in which the court noted the temporal immediacy of the threatened harm, inapposite. The difference in the temporal immediacy between the accident in Irwinand the acts of molestation involved in this case does not dispose the issue of liability. Even though the nine months between Darragh’s placement on probation and the first acts of sexual abuse in this case are much longer than the ten minutes involved in Irwin, the expanded time frame in this case is accompanied by a chronic, persistent, and known threat that Darragh, an identifiable perpetrator, would molest young boys. Where officials know of such a chronic and obvious threat of harm to known *243victims, we do not ascribe a talismanic significance to the temporal immediacy of the harm. Rather, we analyze the temporal immediacy aspect of Irwinin terms of the type of danger at issue. As it concerns driving while under the influence of intoxicating liquor, the time frame involved is necessarily short because alcohol usually has a temporary effect. However, the threat of child sexual abuse is a continuing danger which persists over a longer period.
¶17Moreover, one of the primary reasons for considering temporal immediacy is to determine whether the threatened persons have an opportunity to protect themselves. In Irwin, only the police officers who knew that a drunk driver was on the road were in a position to prevent the harm. The same can be said of Tierney in this case. Tierney was the only person who had the knowledge which could have protected the plaintiffs. See Irwin, supra at 764.
¶18Clearly, the children’s parents could not protect them from Darragh.
¶19*244Although the school officials in this case were in a position to protect these plaintiffs from Darragh, we agree with the conclusion of the judge that the school principal’s failure to respond to a parent’s complaint about suspicious behavior on Darragh’s part is not an intervening, superseding cause of the plaintiffs’ injuries which would relieve the Commonwealth of liability. The failure of a third party to prevent the harm threatened by a defendant’s negligence will not absolve the original wrongdoer of liability. See Mitchell v. Lonergan, 285 Mass. 266 (1934); Farley v. Edward E. Tower Co., 271 Mass. 230 (1930). Moreover, even if we assume negligence on the part of the school principal, only unusual, extraordinary negligence of a third party will excuse an original tortfeasor’s liability. See W.L. Prosser & W.P. Keeton, Torts 312 (5th ed. 1984).
¶20For these reasons, we conclude that Tierney had a duty to these plaintiffs to make a reasonable effort to verify the place of Darragh’s employment. As the judge stated, “other than receiving [Darragh’s] assurances that he was not teaching and was otherwise employed, [the probation officer] did nothing affirmatively to confirm the nature of the non-teaching employment, or to verify that [Darragh] was not in fact teaching within the Commonwealth or elsewhere.” (Footnotes omitted.) Tierney easily could have required Darragh to produce a payroll stub or other evidence of employment which would have alerted the probation officer to Darragh’s deception and could have saved these plaintiffs from the terrible harm inflicted by Darragh. Tierney alone was in a position to avert this tragedy; accordingly, we conclude that Tierney had a duty to make a reasonable effort to verify Darragh’s employment.
¶212. The Commonwealth’s liability. The Commonwealth raises two other arguments as to why it has no liability under the Massachusetts Tort Claims Act.
¶22*245a. Discretionary function. The Massachusetts Tort Claims Act, G. L. c. 258, § 2, provides that “[p]ublic employers shall be liable for injury or loss of property or personal injury or death caused by the negligent or wrongful act or omission of any public employee while acting within the scope of his office or employment, in the same manner and to the same extent as a private individual under like circumstances . . . .” The Act exempts from liability “any claim based upon the exercise or performance or the failure to exercise or perform a discretionary function or duty on the part of a public employer or public employee, acting within the scope of his office or employment, whether or not the discretion involved is abused.” G. L. c. 258, § 10 (b) (1986 ed.). The Commonwealth argues that probation officers’ duties are discretionary within the meaning of G. L. c. 258, § 10 (b). We do not agree.
¶23The Legislature enacted G. L. c. 258, § 10 (b), shortly after our decision in Whitney v. Worcester, 373 Mass. 208 (1977), and we continue to look to the principles enunciated in Whitneyto guide our determinations of the intended scope of G. L. c. 258, § 10 (b). Irwin v. Ware, 392 Mass. 745, 753 (1984). Petrazza v. Commonwealth, 398 Mass. 464, 467 (1986). In Whitneyv. Worcester, supra at 218, we determined that government officials are immune from suit, “[wjhen the particular conduct which caused the injury is one characterized by the high degree of discretion and judgment involved in weighing alternatives and making choices with respect to public policy and planning . . . .’’By contrast, we impose governmental liability “when the particular conduct claimed to be tortious involves . . . the carrying out of previously established policies or plans.” Id.In this case, Tierney failed “to act carefully in accordance with delegated authority.” Cady v. Plymouth-Carver Regional School Dist., 17 Mass. App. Ct. 211, 214 (1983).
¶24There is no reasonable basis to support the Commonwealth’s argument that a probation officer’s duty to monitor a probationer’s compliance with the terms of his or her probation involves policy or planning judgment as defined in Whitney. Rather, policy decisions with respect to a probationer are made *246by the sentencing judge, who places the convicted defendant on probation and sets the terms of the probation. The probation officer’s monitoring of the probationer’s compliance with the probation primarily is an administrative function. We recognize, of course, that probation officers exercise their judgment in carrying out the court’s orders. However, as we noted in Whitney, acts requiring the exercise of judgment do not automatically acquire governmental immunity. “[T]he performance of all functions involves the exercise of discretion and judgment to some degree.” Whitney, supra at 219. As the Appeals Court has noted, Cady, supra at 215, an act is discretionary “[i]f the public employee is required to decide and act without fixed or readily ascertainable standards to fall back upon .... Conversely, if there is a readily ascertainable standard by which the action of the government servant may be measured, whether that standard is written or the product of experience, it is not within the discretionary function exception. ... It requires no manual, for example, to instruct an installer of street lights in Boston that the wind may blow mightily and that lightposts had better be anchored accordingly.” (Citations omitted.) Monitoring the conditions of probation is not a job function a probation officer performs at his or her discretion. It is instead a duty performed in compliance with a probation officer’s obligation to perform such duties “as the court requires.” G. L. c. 276, § 85 (1986 ed.). The statute governing the duties of probation officers clearly establishes a relationship between the court and the probation officer whereby the probation officer is required to fulfil his or her obligations pursuant to the policy decisions of the sentencing judge. A probation officer’s duty to make reasonable efforts to ascertain whether a probationer has complied with the terms of his or her probation is not a discretionary function within the meaning of G. L. c. 258, § 10 (b).
¶25b. Immunity. The Commonwealth contends that the negligent acts of a District Court probation officer may not impose liability on the Commonwealth, because probation officers enjoy absolute immunity from suit when performing duties at the direction of a judge. The Commonwealth relies on our decision *247in Temple v. Marlborough Div. of the Dist. Court Dep’t, 395 Mass. 117, 132 (1985), in which we ruled that judges enjoy immunity from suit if the wrong alleged occurred while the judge was performing a lawfully permitted act within his or her discretion. We also noted that court clerks “enjoy a qualified immunity from suit and are absolutely immune for their conduct when acting at a judge’s direction.” Id. at 133. The Commonwealth contends that the same immunity principles that apply to court clerks should apply to Tierney. We do not agree.
¶26The plaintiffs allege that Tierney negligently failed to verify Darragh’s place of employment. Liability thus is premised on Tierney’s negligent failure properly to follow the court’s directives. The Commonwealth may not invoke Tierney’s possible immunity unless Tierney acted pursuant to a judge’s directive or otherwise in aid of the court. The evidence in this case indicates just the opposite. Any claim to immunity which the Commonwealth might have asserted ceased when Tierney failed to aid in the enforcement of the conditions of Darragh’s probation. See Acevedo v. Pima County Adult Probation Dep’t, 142 Ariz. 319 (1984). For the foregoing reasons, we affirm the judge’s determination that the Commonwealth is liable under G. L. c. 258, § 2, for the negligent acts of Tierney.
¶273. Contribution. The Commonwealth contends that the judge erred in ordering the Commonwealth to contribute $35,000 to the city of Boston. The city settled with the plaintiffs prior to trial; at trial, the Commonwealth was allowed to reduce the amount of each plaintiff’s damages by the amount of the city’s settlement. The jury determined the amount of liability in each case, and, as it happened, the city had paid more than its pro rata share. The judge therefore allowed the city’s motion for contribution.
¶28Contribution among joint tortfeasors is governed by statute. See G. L. c. 23IB, § 1 (a). That statute provides that, “where two or more persons become jointly liable in tort for the same injury to person or property, there shall be a right of contribution among them even though judgment has not been recovered against all or any of them.” As this court has stated, “[t]he contribution statute is aimed at eliminating the unfairness of *248allowing a disproportionate share of a plaintiff’s recovery to be borne by one of several joint tortfeasors. The object to be accomplished is a more equitable distribution of that burden among those liable in tort for the same injury.” McGrath v. Stanley, 397 Mass. 775, 780-781 (1986).
¶29The Commonwealth asserts that third-party defendants are not compelled to contribute a pro rata share of damages to a tortfeasor because a third-party defendant does not share joint liability to the plaintiff.
¶30The Commonwealth also contends that the city is not entitled to recover contribution against the Commonwealth because the amount paid to M.M. in settlement was not reasonable in light of the disparate amounts of the damages awarded to the plaintiffs.
¶31Judgments affirmed.
¶32 Darragh told Tierney that he was employed as a salesman for the National Veterans War Memorial Shrine in Boston. Darragh was an officer of that organization. Tierney checked the telephone directory to ascertain whether the organization existed, but took no additional steps to determine whether Darragh actually worked there.
¶33In March, 1978, the mother witnessed Darragh’s suspicious behavior toward a student in a school hallway. Darragh denied the allegations. School officials held a hearing, but the student did not wish to press charges. The principal did not investigate the matter further, and returned the witness’s written complaint unopened. In November, 1978, M.M.’s mother complained to the principal that Darragh was paying her son an inordinate amount of attention. At that time, Darragh transported M.M. home from school, bought him lunch, and gave him money and gifts. The principal told her not to worry and said there was nothing to be done.
¶34 At the time of trial, A.L. had reached his majority. A.L.’s parents also sued for negligent infliction of emotional distress. These claims were waived before trial.
¶35 At the time of trial, M.M. had reached his majority. His mother pursued her own claim for negligent infliction of emotional distress. The judge directed a verdict for the Commonwealth on the mother’s claim.
¶36 By the terms of the settlement, the city agreed to pay each plaintiff $80,000.
¶37The jury awarded A.L. $130,000 in damages. The jury deducted the city’s settlement of $80,000 from its damage award. The judge ordered the Commonwealth to pay $15,000 to the city. In the case of M.M., the jury awarded $120,000 in damages offset by the $80,000 paid by the city. The city had paid $20,000 more than its pro rata share which the judge ordered the Commonwealth to pay in contribution. In total, the Commonwealth was ordered to pay $35,000 to the city.
¶38 Subsequent cases have followed the Dinskyanalysis. In Ribeiro v. Granby, 395 Mass. 608 (1985), we held that a municipality was not liable for the failure of a building inspector and members of the town’s board of health to require installation of a second means of egress from the decedent’s apartment. We concluded that the case was controlled by Dinsky, and that the town was not liable, because the events transpired at a relatively leisurely pace, and because the owners and the occupants could have taken steps to rectify or to avoid the danger themselves. Ribeiro, supra at 612.
¶39In Nickerson v. Commonwealth, 397 Mass. 476 (1986), we held that the Commonwealth was not liable to an injured motorist for the Registrar of Motor Vehicles’ failure to revoke an individual’s automobile registration for
¶40*240nonpayment of insurance premiums. Applying Dinsky, we held the Commonwealth was not liable, because the Registrar owed no duty to the plaintiff beyond that owed to the public at large, and because there was no risk of immediate and foreseeable harm to a special class of persons who could not protect themselves from it, the hallmark of our analysis in Irwin. Nickerson, supra at 478.
¶41In Appleton v. Hudson, 397 Mass. 812 (1986), the plaintiff brought suit against the town of Hudson, alleging that the selectmen and town administrator had failed to take action against a local club which served liquor to minors. We concluded that the plaintiff could not recover against the town because, unlike Irwin, the town officials had not failed to stop an identifiable perpetrator who presented an immediate risk of harm. Furthermore, we concluded that the municipality’s general duty to provide adequate police protection to neighborhood streets was precisely the type of duty the public duty rule was intended to protect. Appleton, supra at 816.
¶42In Connerty v. Metropolitan Dist. Comm’n, 398 Mass. 140 (1986), we held that the Metropolitan District Commission owed no special duty to the plaintiff, a licensed clam digger, beyond that owed to the public at large, to refrain from contaminating waters in the Commonwealth. We concluded that the Commonwealth’s environmental statutes were intended to protect the general public, the environment, and private landowners whose property was damaged by prohibited discharges, but that no statute created a duty to compensate individuals who harvested shellfish from public waters. Connerty, supra at 145-146.
¶43 One of Darragh’s prior convictions also involved his molesting young boys while a teacher in a public school system other than Boston. The other incidents took place while Darragh was employed at two swimming pools, at least one of which was a Metropolitan District Commission pool.
¶44 Parents, as members of the public, would be denied access to teacher’s criminal record even if they suspected misconduct. See G. L. c. 6, § 172 (1986 ed.), which denies the public access to criminal records and affirmatively provides “a mechanism whereby the fact of a prior conviction is, in most instances, shielded from public view.” New Bedford Standard-Times Publishing Co. v. Clerk of the Third Dist. Court of Bristol, 377 Mass. 404, 412 (1979), quoting Rzeznik v. Chief of Police of Southampton, 374 Mass. 475, 479 (1978). Thus, the parents were not able to prevent harm to their children by ascertaining the teacher’s record.
¶45 We stress the fact that we do not require probation officers to control the behavior of the probationers in their charge. We only require probation officers to make a reasonable effort to ascertain whether probationers have complied with the conditions of their probation and to bring any violations to the sentencing judge’s attention.
¶46 The Commonwealth’s reliance on Liberty Mut. Ins. Co. v. Westerlind, 374 Mass. 524 (1978), is misplaced. That case held that an employer paying workers’ compensation to an employee under the worker’s compensation act, G. L. c. 152, by statute was “released from all tort claims . . . [the employer] might have as a result of [the employee’s] accident.” Id. at 526. That principle is inapplicable where liability is based on the Massachusetts Tort Claims Act and not on the workers’ compensation act.
¶47 General Laws c. 23IB, § 1 (c), provides, “A tortfeasor who enters into a settlement with a claimant shall not be entitled to recover contribution from another tortfeasor in respect to any amount paid in a settlement which is in excess of what was reasonable.”
¶48(concurring). I agree with the reasoning of Justices Abrams, Wilkins, and Liacos, and with the result to which it leads them. I write separately only to emphasize that we today apply, not abrogate, the so-called “public duty” and “special relationship” mies.
¶49The Massachusetts Tort Claims Act (Act), G. L. c. 258 (1986 ed.), provides in § 2 that “[p]ublic employers shall be liable for . . . the negligent or wrongful act or omission of any public employee ... in the same manner and to the same extent as a private individual under like circumstances . . . .” This language does not create any new theories of liability, but simply provides that tort actions brought against governmental entities are governed by the same theories of liability that apply to actions involving private parties. Dinsky v. Framingham, 386 Mass. 801, 804-805 (1982). A problem arises, however, because many governmental functions, e.g., penal incarceration, probation, and parole functions, have no analogues in private.sector law; and others, e.g., police protection, building inspection, have only imperfect analogues. In applying theories of liability derived from private sector law to such traditionally “public” governmental functions, the court understandably has been circumspect. “[F]aimess to the injured individual cannot be the sole controlling factor in this context. Desirable as it might be to structure a system of cost-benefit distribution in which no tortious injuries would go uncompensated, the fact that we are here dealing with governmental entities vastly complicates the issue of the appropriate scope of tort liability. ... An appropriate balance should be stmck between the public interest in fairness to injured persons and in promoting effective government.” Whitney v. Worcester, 373 Mass. 208, 215-216 (1977). That balance has been stmck, in a series of cases, by denying relief where the defendant governmental entity breached a duty owed to the “general public,” and not to the plaintiff as an individual, see Dinskyv. Framingham, supra at 805-806, and its progeny, cited ante at 239 n.8; but granting relief where there is a “special relationship” between the plaintiff and the defendant, see Irwin v. Ware, 392 Mass. 745 (1984).
¶50*250In this case, the plaintiffs have a special relationship to the probation officer which satisfies this requirement and takes this case out of the realm of public duty. This special relationship arose from the highly specific condition of probation that identified a special class of persons (boys in a teacher-pupil relationship with Darragh) within the risk of “immediate and foreseeable physical injury . . . who cannot reasonably protect themselves from it.” Irwin, supra at 756. The plaintiffs, as members of this class intended to be specially protected, were owed a duty of care beyond that owed to the public as a whole. But not every case of recidivism by a probationer or parolee gives rise to liability. Had Darragh molested not a student of the school where he was teaching, but a young boy he encountered at a local playground or in some other extrascholastic context, a different case would be presented. And in the more typical case, the generality of conditions of probation or parole that do not specify an identifiable class of persons intended to be specially benefited does not create a special relationship between the probation or parole officer and any individual member of the public. In the absence of such a special relationship, there is no duty owed, and there may be no recovery against the Commonwealth.