(a) (1) The duty of support imposed by Section 3900 continues as to an unmarried child who has attained 18 years of age, is a full-time high school student, unless excused pursuant to paragraph (2), and who is not self-supporting, until the time the child completes the 12th grade or attains 19 years of age, whichever occurs first.
(2) A child is excused from the requirement to be a full-time high school student for purposes of paragraph (1) if the child has a medical condition documented by a physician that prevents full-time school attendance.
(b) This section does not limit a parent’s ability to agree to provide additional support or the court’s power to inquire whether an agreement to provide additional support has been made.