We do not lock down content based on completion of earlier material. However, you will be able to make steps required, and you can set a minimum required score. Learners will have to complete all required steps and meet all minimum score requirements before being able to complete the course.
While we don't force the order, the order is very strongly encouraged. For instance, the "Next step" button at the bottom of each page is always the next incomplete step. The Path itself opens to the next step for learners to take and collapses past and future lessons. We encourage it so strongly that it's unusual for a learner to go out of order, even though it's not enforced.
You can lock down material by setting dates. Set a start date on access to the course or on the registration window. Or set start dates on individual lessons and steps within the course. This will prevent a learner from viewing or completing a certain lesson or step before the start date is reached.
When using dates, keep in mind that dates are set on the Group and will apply to all learners in that Group.