"or having me come in once a week to clean out his locker"
I am sorry, I really got a good laugh from that! Don't we do enough cleaning up after our kids at home? I know I do! If you managed not to laugh back at them in response to that, you did well (I might not have had the self control). Seriously though, the kids are in school then and part of the program should be for the kids to learn to manage without mom doing it all for them! I think your instincts are 100 percent correct (he has to be accountable, not you).
I am sorry I don't have any info on achievement testing, and honestly we have never succeeded in treating fairly obvious dysgraphia (all three of my sons appear to have that). At a certain age the handwriting is less of an issue (papers are eventually typed). I am only now trying to make my 8 yo understand that writing can be messy and he can take longer to produce it (fine) but that does NOT excuse him from using proper punctuation. I hope you can get helpful responses from others on these issues (and I look forward to hearing about ways of managing the dysgraphia).
I hope you do find some kind of tutor or achievement center option. Surely there is something available nearby (if not in the school), as there is no way your child is the only one struggling with these issues! Good luck, and again I am sorry I can't be helpful about interpretation of scores.
