The following guidelines may not be new but they are almost impossible to implement
“Ensuring that candidates are presented for Courses at the appropriate level, based on reliable and robust judgements of the curriculum level achieved. This, for example, means that pupils should be secure at Curriculum Level 4 prior to starting a National 5 Course; similarly, pupils should be secure at Curriculum Level 3 prior to embarking on a National 4 Course.” from Computing Science Review Document
Where we have mixed ability classes then your N3, N4 students will cover the same theory as your N5 it is not possible to deliver three separate courses. With many students we aim high (N5) then drop down if standards not met and quite often there will be an N3 safety net at the bottom. I encourage and push all my students towards N5 …some need more pushing than others and many don’t quite make it. I would love the time to deliver N4 and assess then move on to N5 but it is not practical in time allocated.