My DS12, dx with ADHD-in, has major problems with punctuation.

He probably has some dsygraphia, or at least a relative weakness in written expression. His VCI is around 140, but his WIAT score for written expression is about 100. He has good spelling, grammar and sentence structure, but terrible punctuation and some problems with organisation of ideas into paragraphs, etc.

Does anyone have advice on exercises or tricks to help him? He will have lots of free time over the summer, and I would like him to work on his writing before he starts middle school next year.

He doesn't seem to notice the "stopping point" where a period is needed, and his capitalization is spotty as well. Sometimes he uses a comma where he should have a period. Often there is no comma when one is needed. It just doesn't come naturally to him, and he is not good at proof-reading his work (partly doesn't want to make the effort, but also because it is hard for him).

I suggested that he read his work out loud and it would be obvious where the periods are needed. He catches some problems this way, but not all.

I'm looking for a fun, entertaining way of helping him with this. He has done exercises adding missing punctuation to texts, and does pretty well at this (although resists doing it because it is "boring"), but he can't seem to apply what he knows to his own writing.