L.R.
If he's bored and resistant you are right to stop.
See if the school has math tutoring -- there may be programs of which you're not aware, right there in his school. Sometimes local high schoolers come into schools to tutor younger kids. Or his math teacher may have ideas.
Kumon tends to be about worksheet after worksheet and (though we have not used it) I know parents who said Kumon meant doing loads of worksheets at home, which both the kids and the parents disliked-- it was just more homework each day. We use Mathnasium instead, which never sends home any worksheets or homework; all work is done during the Mathnasium session itself. My daughter likes doing Mathnasium in the summer (we don't do it in the school year at all). Check them out online.