I went through this same struggle. Every little stress situation caused a cognitive crash. I believe this is all related to his past concussion. I would encourage him to start a vitamin and supplement regimen like listed in the Vitamins and Supplements sticky. It will hopefully help him tolerate stress.

He may need to change the way he studies. Rather than intense study sessions, try to study in short sessions repeated many times. Repetition repeated over time is much better than repetition over a short period. He wants to try to get memory issues past the immediate and short term weak areas.

I wonder about the long term effects of his meds. Learning to study and take tests without them will be a good skill to have.

My best to you both.