¶1The defendant was convicted of eight counts of indecent assault and battery on a child under fourteen; six involving a group of incidents occurring on a single day against one child, and the other two involving a separate incident allegedly occurring four or five months earlier with a different child. With some hesitation, borne principally of the infrequency of instances in our decisional law where convictions have been reversed for improper joinder, we have come to the conclusion that the judge erred in this case by allowing the Com*604monwealth’s motion for joinder of the charges involving the different victims.
¶2The general rule is that “related cases” should be joined for trial unless joinder is not in the best interests of justice. The Rules of Criminal Procedure define “related offenses” as those “based on the same criminal conduct or episode or [which] arise out of a course of criminal conduct or series of criminal episodes connected together or constituting parts of a single scheme or plan.” Mass.R.Crim.P. 9(a)(1), 378 Mass. 859 (1979). See discussion in Commonwealth v. Sullivan, 436 Mass. 799, 802-805 (2002). “[T]he propriety of join[der] . . . turns, in large measure, on whether evidence of the other . . . offenses would have been admissible at a separate trial on each indictment.” Commonwealth v. Mamay, 407 Mass. 412, 417 (1990), citing Commonwealth v. Gallison, 383 Mass. 659, 672 (1981). Such evidence is inadmissible to prove the propensity of the defendant to commit crimes of a type, ibid.-, but it can be used to “show a common scheme, pattern of operation, absence of accident or mistake, identity, intent, or motive.” Commonwealth v. Helfant, 398 Mass. 214, 224 (1986).
¶3Prior reported decisions sanctioning joinder for trial of abuse charges involving different victims (or, alternatively, use of evidence of abuse against a different victim) have hewed to those guidelines. See, e.g., Commonwealth v. Gallison, supra at 671-673 (parents of two young children abused both repeatedly over the same time period); Commonwealth v. King, 387 Mass. 464, 469-473 (1982) (deviant sexual abuse of young siblings during same time period); Commonwealth v. Pope, 392 Mass. 493, 502-503 (1984) (defendant assaulted four women attending convention during one four-hour period); Commonwealth v. Helfant, supra at 226-228 (evidence admissible of physician’s prior use of Valium injections to weaken female patients’ resistance to abuse); Commonwealth v. Mamay, supra at 416-417 (defendant, a gynecologist, employing unorthodox examination positions, fondled patients on the examination table); Commonwealth v. Feijoo, 419 Mass. 486, 494-495 (1995) (karate instructor teaching adolescent boys that part of becoming a Ninja warrior involves ritual of participation in intimate relations with instructor). Apart from the cases involving an unusual *605or distinctive modus operandi (like Helfant, Mamay and Feijoo), the cases in which joinder was approved often emphasize proximity in time as a critical element. Thus, in Gallison, the court reasoned that the abuse of the younger brother of the victim named in the indictment a nine year old female was admissible because it was similar in pattern and occurred, over the same time period, thus “form[ing] a temporal and schematic nexus with the treatment of [the sister].” Commonwealth v. Gallison, supra at 673. The Kingdecision, recognizing that it would be the first case in which that court permitted “evidence of a defendant’s sexual conduct with a child not named in the indictment [to be admitted] in an action charging a sexual offense against the named child” (Commonwealth v. King, supra at 471), emphasized that the evidence fit the “temporal and schematic nexus” formulation of Gallison; that is to say, “both children lived in the same house with the defendant, the sexual acts took place during the same time period, the victims were of similar age (both under ten), and the form of the sexual conduct (oral sex and use of the dog) was similar. These factors make this evidence distinguishable from the unconnected acts we excluded in [Commonwealth v.] Welcome, [348 Mass. 68, 70 (1964)].”
¶4As joined, the instant case involved thirteen year old classmates of the defendant’s daughter, Anne,
¶5The second complaint involved Rose,
¶6These cases should not have been joined for trial. Evidence of the defendant’s conduct with Kathy would have been inadmissible in the case based on Rose’s allegations; so too, evidence of his conduct with Rose, in the case based on Kathy’s allegations. See Commonwealth v. Barrett, 418 Mass. 788, 794 (1994); Commonwealth v. Jacobs, 52 Mass. App. Ct. 38, 42-43 (2001). In contrast to evidence of earlier bad acts involving the same parties, which is often “relevant to show the probable existence of the same passion or emotion at the time in issue,” Commonwealth v. King, 387 Mass, at 470, quoting Commonwealth v. Bemis, 242 Mass. 582, 585 (1922), evidence of bad acts “by the defendant toward a child other than the complainant . . . , to be admissible, must be closely related in time, place, and form of acts to show a common course of conduct by the defendant toward the two children so as to be logically probative.” Commonwealth v. Barrett, supra at 794, citing the Kingand Gallisoncases. “In other words, the conduct towards the children must form a ‘temporal and schematic nexus’ which renders the evidence admissible to show a common course of conduct regarding the two children.” Ibid.See also Commonwealth v. Cogswell, 31 Mass. App. Ct. 691, 696 (1991) (defendant abusing stepdaughters repeatedly, inducing silence by identical threats); Commonwealth v. Lanning, 32 Mass. App. Ct. 279, 283 (1992) (defendant, close family friend, in continuing pattern of sexual abuse of daughters from age nine on).
¶7As the trial judge observed, there were many similarities between the alleged assaults against Kathy and Rose. The victims were both schoolmates of the defendant’s daughter. Both were sleeping over at her house. Both were assaulted at roughly the same time at night, and the defendant’s alleged advances in both cases consisted of fondling breasts, vaginal areas, and buttocks. “The alleged offenses and their circumstances were thus undoubtedly similar. . . in major respects. *608However, they were not ‘related’ within the meaning of Mass.R.Crim.P. 9(a)(1), unless the judge could conclude that they arose ‘out of a course of criminal conduct or series of criminal episodes connected together or constituting parts of a single scheme or plan.’ ” Commonwealth v. Sylvester, 388 Mass. 749, 755 (1983).
¶8The judge could not properly so conclude. The acts were plainly not a part of a single course of criminal conduct but rather were separate acts involving different victims four or five months apart. The acts were not connected together and were not part of a single scheme or plan. Nor did the evidence bring the case within the mold of the modus operandi, or pattern of conduct line of cases, such as Helfant, supra;Mamay, supra; Feijoo, supra; Commonwealth v. Odell, 34 Mass. App. Ct. 100, 103 (1993) (defendant stupefying numerous women with drugs and alcohol), or Commonwealth v. Hanlon, 44 Mass. App. Ct. 810, 819-821 (1998) (priest taking altar boys to ski lodge).
¶9Judgments reversed.
¶10Verdicts set aside.
¶11The Welcomecase was a prosecution for the defendant’s alleged indecent assault on a female child. The court reversed the conviction because the judge had admitted evidence that the defendant had previously assaulted other female children. “We invoke the rule that evidence of a distinct crime unconnected with that for which the defendant is indicted cannot be received. An exception to this rule is stated in Commonwealth v. Machado, 339 Mass. 713 [1959], where there was evidence of prior illicit sexual intercourse between the same parties. In the present case the testimony related to earlier misconduct by the defendant with other parties.” Commonwealth v. Welcome, supra at 70-71.
¶12A pseudonym.
¶13Also a pseudonym.
¶14A pseudonym.
¶15Rose testified: “Well, our conversation kind of consisted of well, it happened to me, too, I told her; so you’re not alone. And then we became friends, and she asked me if I would come forward, and I said yes.”
¶16There is an extensive and useful discussion of the relationship between the “temporal and schematic” and the “common pattern” lines of cases in Commonwealth v. Hanlon, 44 Mass. App. Ct. at 816-821. See Commonwealth v. Jacobs, 52 Mass. App. Ct. at 39-47.