I tutor from home and feel that it can be detrimental for children to have extra lessons if they are not eager. Everyone has stages where they are really interested in something then lose interest. If you son is a high achiever (even if he was an average achiever) he can enjoy maths in an informal setting, it is not necessary for him to have extra lessons. There are many maths concepts that children can gain through playing. Make it a game - in the garden if each flower has ten petals how many petals do you think there could be on 4 flowers? When going up or down stairs count is 2's, 5's 10's , every now and again say '25 so how many steps do you think we have come up?' How far do you think it is to the end of the garden? Let's measure it together. Make sure you guess with him and obviously get some right but get some wrong and laugh about it. It is important that you are relaxed and make it fun. Just every so often ask a question if he is keen then a little later ask another but do not over do it. Children learn best when they are having fun, keep him wanting more. Good luck