Based on a true story (you can find the news accounts on-line), the story details deviate from the record, but stay true to the general plot-line A psychopathic maniac has a grudge against the town, and a belief that he will be resurrected after detonating the bomb,
with the hostage children as his subjects. The bomb detonates accidently; he shoots his wife after she is engulfed in flames, then kills himself. The children (a large number if not all; the reports are unclear) testify that angels told them what to do and channeled the blast away from them. A bomb expert concurs that what happened is impossible -- no one but the perps died in the blast, the fire, or the randomly detonating ammunition, including the teacher shot in the back.
The movie script, focuses on the (real-life) hard-headed sheriff's investigator with kids at the school, who has lost his faith in God (not clear if that is true or a plot device, but it gives the writer a chance to "investigate" the explosion).
The children are shown as praying during the ordeal and the whole town as faithful Christians, but it obscures the fact that most were Latter-day Saints (Mormons); however, no one else sings the song presented in the denouement, or has buildings and pictures exactly like those depicted, so there you are. ( )