I can't say I've had fantastic success. Ds2 loved maths and did it for fun at home using online programs in year 1 & 2. Now in year 7, he isn't that keen on maths lessons, but I think it is because he associates it with boredom.
I've noticed that he still finds it absorbing when he is learning something new (he has a habit of trying to grab DS1's books). However, I think part of this is just trying to prove that he is better at maths than DS1 - who is top of his year for maths himself, so its quite a target Ds2 appears to have set himself.
Things to do... chess, programming, books like Murderous Maths or Think of a Number. Showing an interest, but biting hard on your tongue when he only gets 99%. (I am a bit inclined to want to turn to see what one he got wrong rather than plough through the ones he got right). I used IXl for a while but after KS1 the boys stopped wanting to do it.
Oh... and the favourite car game... I ask a question and they take turns in answering them e.g. name the next three numbers in this sequence e.g. 17,19, 23, 29,... or 1, 8, 27,... These days I make them do simultaneous equations in their heads but they still beg me to ask more questions.