MathGames

MathGames by TeachMe
  https://www.mathgames.com/
 
MathGames is a kid-friendly source for math practice, standards and worksheets.
You can select for grade and skill(s). It is easy to navigate and gives positive reinforcement as well as chances to try again. 
I selected 6th grade. I tried a couple of the skills. There are 16 options for skills ... super!
This resource is free. It appears that if you sign up you can select to not have ads. I did not sign up and was still able to navigate the site without ads.
The site graphics are colorful and non-threatening.

About MathGames: MathGames.com, by TeachMe, is an online suite of internet math games, available for teachers, students, and parents to use inside and outside the classroom. Covering math concepts in Pre-K to 9th grade and searchable by Common Core State Standards, The site also has progress reports and dashboards for parents and teachers to track individual student performance.