Have you heard of Splash Math? It's a great common core math app for all grade levels 1-5.
You can start with the free lite version and gets lots of use from it. Here's a look at some of the concepts taught in the 2nd & 3rd grade versions:
It gives immediate feedback.
Here's a list of skills available in the paid version (2nd grade):
I love the scratch pad feature at the bottom of the screen.
A must have app for common core math instruction!
Blessings to you,