This is a great letter recognition, word recognition and reading app for that age group that has a great variety of mini games that handle progression, fight boredom. I wish it had math because I think the quality is great.

Smarty Pants School

https://itunes.apple.com/us/app/smarty-pants-school/id403824279?mt=8

While I'm happy to see this as an end user - they did have good applications as well. They were a great mechanism for tracking fraudsters across cookie wipes... The more savvy ones knew better but for those who didn't it saved us a lot of losses...