Question

your friend has heal the problems but doesn't share or explain this to his /her teacher or classmate. he is of an absent school and is not able to perform well in exam discuss with your partner

Answer 1

you could try to counsel him 

maybe you can take him to some elder or counselor for his aid

always try to make him feel comfortable when others are around so that he doesn't feel insecure about his health problems

also make his classteacher aware about the fact and ask her for further actions  towards his comfort