Just to share my friend's story with you: My friend's boy starts Kumon since K1, and non-stop till now. He's k3 now. Well, he disliked that in the beginning and his mom "forced" him to finish the hw (eng, chin (pth)& math) daily (really tough for both mom & the kid), but after a long long while, he started to like them and his progess is good too. Now, he does Kumon exercise daily by himself or under the helper's supervision.
Since I've never attended any talk about Kumon, so no advice to you. Also, Rachel's schedule is already very packed now