Have a look at Whizz.com for maths. It covers the National Curriculum and you initially do an assessment which tests roughly where you might be.
It is very thorough and covers everything they need to know but it is strict in that the tutorial sets the lessons you learn, and you have to do them to move on. This means the whole curriculum gets taught.
You can replay all the lessons so this helps with the understanding. Sometimes kids pass the exercise because the questions follow a formula but dont really understand it, so by repeating the lesson they sometimes understand it better next time.
In addition, you can compete against other uses to improve your times.
This part is in the lesson order.
There is also a topic revision section which breaks down each topic into approx 17 sections so you can replay all the lessons up to four age levels back. Lessons go up in 1/4 year scales.
Sometimes parents are not happy because the lessons seem easy, but it is better to start off easy because there will be topics that the kids just havent covered at school, and it formalises the teaching process so that they remember it.
Whizz recommends a minimum of 60 minutes a week to progress but if you allow 90 minutes you can really make headway and move forward.
negatives are there are no worksheets to print, it is all computer based. Also, if you are covering a specific topic at school and you havent done it yet on Whizz you cant learn about it and have to find alternative resources. You can however, relearn the basics of that topic through the revision section.
A few people like Mathletics which also covers the curriculum but the presentation is very different.