Is it forbidden to delay the Ishā’ prayer until the following morning, if the time for Ishā’ extends very late into the night and there is a commitment to school early in the morning?

It is not permissible to delay the Isha prayer beyond its prescribed time. Whoever does so is sinful and has committed a grave sin, for Allah Almighty says: "Indeed, prayer has been decreed upon the believers a time-bound ordinance" (Quran 4:103). You must pray on time and advise your parents of the necessity for you to stay awake to perform the prayer, and to utilize a midday nap (qailulah). Even though the Prophet, peace and blessings be upon him, forbade sleeping before Isha so that the prayer would not be missed, if your parents force you to sleep, do not obey them, even if you pretend to sleep until the time of prayer.