I am a tutor and a parent.
These sites I use a lot for my work:
MEP Mathematics Enhancement Programme - extensive & free:
Mathwords - a very thorough dictionary:
My daughter has used these (although a little bit expensive), but she was very pleased with the approach:
GCSE Maths Revision Cards
Hope this is useful.
I am now looking for a website which does good practice for common entrance tests for ages 10,11 and 12. Any ideas ?