HI!
sorry for my previous reply, pls ignore it was just a misprint.
if positional turn means similar to BPPV or any disorders due to impaired vestibular system, then
8o i would first like to know what were the previous symptoms for which he received physio treatment.
8o was there any significant history at the time of birth or any infections, fever,falls/injury, anemia,bleeding, medications given to mother during pregnancy which might affect neurodevelopment in the child.

when you say your child has difficulty in playing sports or writing it suggests problems with balance, eye-hand co-ordintion, muscle imbalance(co-contraction/reciprocal activation), visual affection, visual perceptual deficits, posture etc. any of these could cause difficulties which you have mentioned. if you get more specific as to what are the difficulties he faces while writing or while playing sports(falls/weakness...) it will be easier to target where the problem lies and accordingly formulate the treatment.

hope my input is of some help. hope to hear from other members.