Here's a web site you will fall in love with, even if you did not enjoy maths when you were a kid. Especially if you did not enjoy maths as a kid.
And if you have a child who is studying right now, then please, please, please do that child a favour. Go to this wonderful site and let his/her just spend lots and lots of time here.
Maths can be fun too, you know.
Take a look at murderous maths.
And if your child falls in love with maths and school grades improve drastically, do not forget to thank me.