In Coassemble, there are a couple of scenarios where your learners' can be locked out of a course.
A course availability date is set in the future
As a trainer, you can set a date you want your course to be available from. If you set a date that is in the future, learners will not be able to access the course. The course card on their dashboard will include a lock icon, and the date that the course will be available.
A Course has prerequisites
As a trainer you can set up course prerequisites which will force your learners to complete one or more courses before they can start a new one. Similar to course availability, courses with prerequisites will include a lock icon, but will display the name of the course, or multiple courses they must complete before they can access the current course.