Kumon woes

We should start a Kumon Parent support group for over achieving parents like us! It is a daily battle at our house esp. with the younger one. The older one is better at it nowadays. At one point, he used to shed tears at the very mention of the word. Now, we have made a deal. He only does his work at Kumon and I stop bothering him during the week. I have to sit with S, appeal to his good senses, cajole him and finally threaten him with consequences, when amid tears he will take out his Kumon folder.
I also have to constantly check on him to ensure he is not drawing eyes and ears to his numbers or sitting with his back facing the Kumon.
I've tried several methods such as "a constant/dedicated time", a quiet place, isolation, standing looking over his work.. nothing works. My resolve weakens before his does.

I've been coming home pretty late all last week. I return home late last Thursday evening and enquire about the younger one's homework and the conversation goes along the lines of:
Me: "S, how's your homework comin' along?"
S: "All done!"
S does not get much homework.. so I think that it must've been a day he had a substitute or they had a test..
Me: "Start on your Kumon. You have to do two days worth"
S: "Done -both days"
I'm pleasantly surprised.. thinking to myself.. Finally, S is getting responsible..
Me: "That's great S! I'm glad you did your Kumon!"
S: "Appa Made Me!"

There was a lot of feeling in the last remark... Hopefully all this effort is worth something in the long run!