The completion of one Lessons page or subpage before allowing students to move on to subsequent Lessons pages or subpages in the Lessons hierarchy can be set as a requirement. That is, instructors can require that all of the required items on one page be completed before students have access to subsequent Lessons pages or subpages.
Go to Lessons.

Select Lessons in the site Tool Menu to display the page.
Select the Settings icon from the action menu.

Select the gear icon to reveal the Settings menu.
Require Lessons page and Save.

See How do I require completion of a Lessons item? for directions on requiring an item to be completed.
Note: Required items are indicated by an asterisk.
See How do I require completion of a Lessons item? for directions on conditionally releasing an item based on prerequisites.
If a student selects the subpage link or button without completing all the required items on the page, nothing will happen. (Instructors can click on the subpage link and the subpage will be displayed.)
Note: The subpage link (or button) now displays the text [Has Prerequisites] next to the item.