Beestar

We were referred to http://www.beestar.org/by a friend. Turns out to be quite a treasure trove. They have Math and Reading worksheets for K-8. We signed up for the free version that allows one access to 2 worksheets per week. The first grade Math worksheets are not easy, to put it mildly. They cover a variety of concepts such as "read clock, place value, simple patterns, problem solving methods, describe individual coins, understand real object graphs, skip count, unit sense, apply simple addition facts, addition/subtraction patterns, compare small numbers, etc". This is a huge improvement over say, Kumon, worksheets that tend to be very uni-dimensional.

Again, this is not a site that teaches concepts but tests concepts. They do provide a list of reference books that could be used offline.

I am still on the quest for finding sites that not just test but also teach in a fun way. Of course, it would be nice if those sites were free and great at capturing the imagination of young children. :)