It's easy to unpublish / withdraw student reports from Pupil Progress App.
When you withdraw reports parents will no longer be able to see them in Pupil Progress App.
To withdraw reports:
Login to Pupil Progress and go to Reports > App Reports
Find the relevant report
Click the Delete button to the right hand side of the report details
Note that if you are publishing new reports, you don't need to unpublish previous reports unless you want to. Older reports will be clearly labelled as "Past Reports" in Pupil Progress App.