Can I create one report to show internal assessment data for all Pupil Premium students in the school (or other cohorts)?

Head to Reporting>Assessment>Steps (tab)>Checkpoints. Select the subject you wish to report on, from the Cohorts dropdown select Pupil Premium. Click Choose and you will get a table of all students in the school who are eligible for Pupil Premium, with their internal assessment marks. This will work for other Cohorts should you wish to report on them.