Several things to check:
What layout parts have you created and how are you sorting the records?
You should have:
--SubSummary when sorted by School--
Student Name Field
Your records should be sorted by the school field (You can specify the student name field as the second field in the sort order to alphabetize them.)
If you have all that and still don't see a change:
Any chance your student name field is a pixel or two too high? If even one pixel of the name field crosses the line into the subsummary part, it'll be treated as part of the subsummary and this may keep the subsequent student names from appearing. If you think this is possible, enter layout mode, click the field and use the down arrow key to "nudge" the field down a pixel or two and see if that fixes the issue.
Thank you, PhilModJunk. This was helpful.