"We've had some luck and engagement with SumDog Math - www.sumdog.com
"Sumdog's learning engine adapts its questions to each student's ability helping teachers deliver Common Core State Standards. Aimed at grades 1 through 8,…"
"Go to mathlanding.org. It is a new website of vetted elementary math resources aggregated from the web. And everything is free. The search engine is easy to use and there are lots of ways to find resources--advanced search is great and…"