Before you pay for anything - explore the free stuff! Does he already use the BBC Bitesize sites? Also try Mr Barton's notes, maybe the interactive tutorials on CIMT? Math is fun... Links all here. Does his school use Sumdog? He might enjoy the numeracy games. He can sign up himself free if the school does not subscribe. I wrote some instructions for our students here and there is plenty of help on the Sumdog site. For more games he might enjoy Manga High.