In the new academic year pupils and their classes are updated in Sonar to reflect where they should be in September.
If the pupils in a class are exactly the same as in the previous year you can often change the term and the year within a report to a different point in time.
If the children are different; some may have left, some may have joined, the year group may have been mixed up, you will have to make a group of the pupils you wish to see data for.