Setting the book range students see

In the Edit Course dialog, set the range of books students see by planet (level), and narrow it within a planet by Form (steps of about 50L). A range spanning several planets can pin a Form at each end.

Per-student

If a student needs a different range, open the range popover on their row in the course Roster and choose "Save override" or "Use course default".

Note: from the roster you override a student's allowed book range — not their Lexile reading level. Editing the Lexile level itself is done on the admin student page.