Hi, since how long has he been experiencing problem with concentration? There can be two possibilities here: one that he always had an issue with attention and that could be due to ADHD/ADD or if he has recently starting facing this issue then it could be due to his anxiety for his CS exams. You should ask him to visit a counselor for a more accurate assessment and a few sessions will also help him to vent out his stress for exam. And for the time being, he can try some relaxation techniques like deep breathing, meditation, running or listening to soothing instrumental music. Counseling will help him more as he can learn to cope with stress in a systematic manner.