Study Island can be good for acceleration, but the progress serves more as an assessment tool, rather than instructional tool.
I use Study Island for Kindergarten prep/acceleration (along with other programs). Students are provided with links and resources to learn the content, then they play the games on Study Island.
The kids seem to like Study Island, especially being able to skip around to different topics.
Study Island has a pretest & posttest, so you may want to test your son to see if he already knows the content. I set the mastery level at 90% for all courses, but that can be modified to fit your situation.
