Summer Program for processing speed | ADHD Information

I'm thinking about having my son do a summer program of some sort to help him improve processing speed and attention, but mainly processing speed.

He has done interactive metronome, and it did help him improve in coordination.

I've been reading about PACE and Fast Forward. He reads past grade level, but he has touble finishing tests, especially math and science this year- any tests which require a lot of writing. He gets the extra time he needs (which is usually less than 40 min.) now through the 504, but wouldn't it be great if we could help him to process faster?
Thanks for any suggestions!