It does look like his writing problems dramatically lowered his processing speed score...
The working memory test being so high really makes me doubt ADHD... it's a super boring test of just listening to someone rattle off numbers/letters and repeating them back either forwards or backwards, depending on the test.
With Coding, symbol search and picture concepts all being low, I'm curious, has he been to a pediatric opthamologist for a proper eye exam? I'm wondering if he's actually maybe having trouble seeing clearly...