My Year 6 DS is also supposed to be sitting a level 6 paper but I am coming at this from a different angle from you. As Guest55 says, this is material for secondary school. If a primary school wants to make itself look good by putting children in for level 6 then I reckon they get to take the rap and do the teaching for it. Personally I am against it...why would you want to practice stuff he isn't really meant to be doing until next year? SATs are for schools: not children, not parents.
If you do want to practice after all that...the papers you will get with the link Araucana has provided are indeed secondary ones which will provide masses more than you need, and possibly scare the poor child too! From what I can tell, 'level 6' at primary school involves a couple of questions on limited topics which do not really equate to a solid level 6 at secondary...perhaps Guest55 could clarify? And I am afraid I can't help with your query, as I would not do SATs practice at home.
Sorry G55, our posts crossed