Getting an assessment is a good idea for several reasons. Heading back into public school (and into SAT/ACT/etc) you'll need the assessment if you want accommodations. If organization is identified as a challenge, then you should be able to get him help with his organization skills that will help ease the transition back into public hs.
Also important (jmo) is that an assessment can help you understand the root cause of what's driving the issue with organization (or whatever). That understanding is not only going to help with school, but with life
My only caveat here - I'd try not to make the diagnosis myself first, then seek out an assessment only looking for that. There are a lot of issues that can cause symptoms that *look* like ADHD but aren't. I would want to rule out other potential causes before assuming what you are dealing with is ADHD.
Best wishes,
polarbear
