MathGames.com sounds like it is just another website hosting math games for kids. Scroll down below the games and you will find dozens of practice exercises aligned to K-8 Common Core math standards. On each exercise page students will find a virtual scratch pad on which they can work out the answers to the problems presented to them. On some of the exercises students will be shown an explanation of the correct answer if they have answered incorrectly.
To access the practice activities on MathGames.com scroll past the games section and select a grade level. After choosing a grade you will be taken to a complete list of the Common Core math standards for that grade. Choose any of the standards and a set of ten practice problems for that standard will appear on your screen.
Applications for Education
MathGames.com offers a teacher dashboard service through which you can view students' progress. You can register for a teacher account through Edmodo, with your Google account, or you can create an account with your email address.