In the Teacher Dashboard, under the My Classes tab, select the class you wish to lock modules or levels for. In the class page, select a chapter from the Select Chapter drop-down (next to the Curriculum Guide button), checkmark the box next to a student's name (or checkmark the box next to All Students to select all students in the class), then hover your mouse over a module's padlock icon 
and select Lock to lock all the levels in that module. Alternatively, you can lock individual levels by hovering over a level icon in the column and selecting Lock. Locked modules and levels can be identified by the 
icon.