poor memory is due to lack of concentration.some people easily grasp what teacher has told and some wont this is due to not keeping their full pledge interest on what they r say.mediation which increases the concentration level.some students in class they wont listen lectures their mind will be roaming some where else.may be in the begining they may pay attention but after few minutes they lose the attention.meditation can increses these attention and concentration.
meditation is nothing but paying attention on breath
Apart from meditation give him some good health drink and protien rich food. He will improve. Sit with him for sometime when he studies to see that he is studying well and not getting distracted.