Sorry to hear that your DS is unhappy at school. The teacher makes such a big difference. The older grades are easier in that respect.
It's great that your school already provides him with reading at his level. Lots of schools say that they do that, and then hold the child back to some preconcieved notion of what a strong X grade reader could possibly do. My son's 4th grade teacher noted that he was reading 4 levels above what any 4th grade kid at his school had ever placed into, and that she was placing him in the top reading group with kids 4 levels behind him and giving all of them material 2 levels behind him, so that he would have a group of kids to be in reading group with. Sometimes teachers stop testing at 2 levels above grade level and report that as the child's level.
I think seeking Math that allows him to move at his own pace is a great idea. I don't see that a WJ Broad math of 136 is in any way 'bad' enough to block a kid from doing Math at his own pace. (Doesn't it make sence for all kids to do math at their own pace?) 136 is well into the gifted range and well above average. It might look bad next to 151, but that just means his potential is 'wow-wow gifted' and his output is only 'regular strongly gifted.' This is quite normal for PG kids with ADHD. It doesn't suprise me that the testing report was full of qualifications because how often does a tester get to write a report about a kid with a 151 PRI (which only vaugly corresponds to Math, BTW, it corresponds to problem solving in general - fluid knowledge, that is 'stuff you haven't been taught.')
BTW - if you want to post all his scores, we can give more insight. We see scores like 151 PRI quite frequently - such is the marvel of the Internet.
Welcome,
Grinity