My DD8 does EPGY (open enrollment) during her class math time in second grade (public school). The only downside is that the teacher understandably can't do a lot of one-on-one time if my DD has a question. But EPGY's allowed her to go more at her own pace, and for the most part she likes it.

The teacher (who has been wonderfully accommodating) has also allowed her to work on other math Web sites that help with math fact speed.

So, bottom line--I think it's a great idea!