To have a health problem could be any type! And especially the child is not willing to share it therefore it could get dangerous too!
Suppose if the child is having something like dyslexia or dyscalculia etc he must receive better treatment! And to receive better treatment, the child should cooperate sincerely; if he had to cooperate/ open up then it's required to provide him with a personal counselor! the child avoid sharing his health problems with others because he fears embarrassment! Counseling can solve that problem!
Open up to him about his health and always give him support and hope!
talk with his parents! in case he is showing any symptoms the first one to know about it will be his parents! Convince them that the child need immediate attention or else his health could decline!
Next step is at school; the child may be financially broken and that could be why he maintain silence, so raise a fund to help your friend! friends are for the hard and tough times, aren't they?
Teachers could provide him extra classes and help him attend special classes! Visit him if he is in the hospital or just spend some time with him at least!
always let him know your support, that's when he'll feel confident about himself!
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