If he knows his numbers and can count to ten, you can start him on math. That’ll really challenge him. We let Ginny use pennies to help, and she’s up to 20 sums in addition, and we just started her at subtraction. (she’s 5 and a half) My web site at http://looklistenlearn.org/learn/math/ can be a big help since it generates the math pages for you and even grades them. Ginny’s been doing it for fun and my boys used to use it for their homeschooling until they got passed what it could do.