We have classes set according to ability across two year groups e.g. Top Set Maths from a mix 7 and 8. After seeking support we discovered that only forms can be mixed across year groups. You are able to create sets in teacher manager across multiple year groups. However, if you then try and register this 'set' because they are mixed year groups it will not appear. Form groups can be registered when they are set as vertical groups.
Please allow mixed year sets to be recognised in the registration manager. More and more schools are going to stage not age.