Data on ScholarPack is stored against the Student and not the Year/Form they were in at the time.
When you run a report, lets take an attendance one for example, there is often a date range you can choose. This is what is going to tell the system what data it needs to pull through.
So lets take a Y3 student. You want to find out what their attednance figure was in Y2.
Find an attendance report and choose Y3, but put the Date to the period you're wanting to report on.
Now when you run the report, the Students will show in their current year/form but the data will be for the date range chosen.