I don't know much about the RSM, but I know a bit about Kumon, as I had my eldest tested there when he was 7 or 8.
The elementary-level program is all about memorization and mastery. The kids have to complete long worksheets that repeat the same type of problem over and over (and over...) again, until they can finish one in less than x minutes without errors. Both conditions must be met in order to move forward. Apparently, the idea is to deliberately start kids at a very low level, so that they can "progress quickly," whatever that means in this context (from one set of worksheets to a slightly more difficult set of worksheets?).
Here's a
plain language analysis of the Kumon method, written by someone who ran a center for a couple years.
Overall, Kumon is probably an excellent training ground for those desirous of acing high-stakes tests (or their children). I don't think it's right kind of place to develop mathematical talent, though it may well be the sort of place that can help develop compliance.
