I am a secondary teacher who did work with Year 6 (and 5 and 4 and 3!) children at a local primary, leading to a few sessions of Level 6 coverage in the 2nd half of the spring term. I also marked them for the STA this year. Firstly, most importantly, do not say anything to the students about it until well after Christmas. It is NOT important and they do not need to be stressed about it. When you do, explain that it is not part of the SATS, it is an extra test just to see what they can do - it is not pass or fail and it will not affect their future. You should not try to cover everything at Level 6 - your focus should be to get them as confident on Level 5 work as you can. Level 6 is a bonus, and you should pick a few key topics to cover, e.g. trial and improvement, ratio, probability. I could go on but will stop there for now.