ConquerMaths is a virtual tutor that helps you get better at maths. Covering subjects ranging from algebra to trigonometry, the lessons are mainly geared towards pupils aged 11-16 (i.e. up to GCSE exams) though really they're open to anyone who wants to become more numerate.
BBC online did a feature on Conquer Maths saying that a Teeside school doubled its GCSE pass rate because of it and pupils even logged in on Christmas Day! Sounds like a solution for parents who think their child needs to be getting better grades in maths.