The sooner you to get him to make the attempt, the more comfortable he will feel about drawing and writing in public. My son is in first grade and refuses to do any writing at school.However he is now comfortable enough to write at home.It took alot of time and patients.
The only thing that got my son to write was using his favorite subject as an incentive.In my son's case it is easier to write sentances,numbers and letters,than drawing.Its not that he cann't, he is too self critical when drawing.
-I would start with tracing.(he cann't make a mess when tracing)
-Have him mix colors together with a paintbrush.
(this may make him more comfortable with the idea of holding a pensil.
-Will he draw with chalk on your driveway?maybe not? But worth a try.
My perfectionist son has always like to practice things in private.It sounds like your son is doing this with reading.
