Appointment of a surrogate parent shall be effective until the child reaches eighteen years of age, provided the Commissioner of Education, not less than thirty days prior to the child’s eighteenth birthday, may extend such appointment until the child graduates from high school or reaches the age of twenty-one years, whichever occurs first. If the surrogate parent resigns or dies or for any other reason is unable to continue as surrogate parent for the child, the Commissioner of Education shall, if said commissioner deems the appointment of a successor surrogate necessary, appoint a successor surrogate parent.