First, check that Year End has actually been completed by going to Admin > Year End. It ought to say:
If it hasn't been completed, follow the steps until it's finalised and students have been promoted to their new Form groups and Years.
If Year End has been completed, check your Form groups at Reporting > Reports > Students (blue tab) > Current Form Groups.
Split the report by Form (or year and form), tick to include Current and Future Students, then select Choose to check your Form lists.
If any Forms or Year groups are incorrect for a small number of students, you can amend them individually on the extended tab of the student profile.
Alternatively to update the students in bulk please go to Admin > Students > Group Updater, change the year and form to the current year and form the students are assigned to and change the student attribute to either "Current Year Group" or "Current Form Group" depending on which needs to be amended.
Click "Choose" to display the students in that year group, and then select the Form you wish to place them in for the academic year.
Click "Check All", and then Update at the base of the page to save this new Form allocation.
Occasionally there is a problem caused by Forms having very similar names to ones used the previous year. If you go to Admin > Config > Core Setup > Forms, check that each Form has a unique Abbreviation and Description.
Any duplication here will cause problems with the Forms setup and the reports. You will need to edit and rename any Form which has been duplicated in either the description or abbreviation, then head to Group Updater to ensure the students have been assigned to the correct Form for this academic year. It will be easy to identify which Form you need once the names have been changed. It is advisable then to return to the Forms setup area and delete the old forms so they no longer appear in the Forms dropdown in reports and the register area.