Children Math Game

Hi guys, it is an application for children who want to practice their math by themselves or with friends. Also teacher can create math groups for their students. I designed it 2 years ago.
Here is the prototype link:
https://invis.io/AHS1LNSJK3S

And app store link:
https://itunes.apple.com/vn/app/matevo/id1321846265?mt=8

All the best. Thank you.