I'm trying to figure out what to do with my son to help him find more challenging math. He's 8., 3rd grade, tests at an 8th grade level, but I'm not sure that I would start him off with 8th grade math.

Can anyone rec a book/series? Online program or app? Or enrichment program?

He's bored and disengaged at school, and I want to provide him with something that will challenge him and keep him learning. Thanks.