IXL

In the Grade 6:
Under the title "Number Theory"
Practice:
N4: Identify Factors and N7: Greatest Common Factor

In Grade 7:
Under the title "Number Theory"
Practice:
A4: Divisibility Rules and A5: Greatest Common Factor

In Grade 8:
Under the title "Number Theory"
Practice:
A1: Factors, A2: Divisibility Rules and A5: Greatest Common Factor

Enjoy!