My children were really struggling with their math skills. They hated timed tests because, being very competitive, they were falling behind others and wanted to always be at the top. I began searching for "good" timed test apps since they enjoy using my ipad. This app (which I later purchased the full version of) has taken my daughter from the middle of her math class to one of the top 5. She competes with herself nightly to see if she can beat the night before. It has the same layout as what she uses at home but it is on the ipad which must mean it is fun.
This app is free but there is a paid app with more math skills.