What should a student do regarding his classmates who openly insult religion at school, given his inability to change the wrongdoing and his fear of the consequences of confronting them?

Reviling the religion is apostasy from Islam. One must denounce the perpetrator to the best of their ability, for enjoining what is right and forbidding what is wrong is obligatory upon every Muslim according to their capacity. A Muslim must speak the truth and not fear the blame of any blamer, and be patient in the face of what they encounter. If you are compelled to remain in a gathering where wrongdoing is committed, then you must denounce it with your tongue. If you are unable, then you must denounce it with your heart and detest it, and there is no sin upon you for remaining then, for Allah does not burden a soul beyond its capacity. Gentleness and kindness should be employed in denunciation and invitation.