If your school or studio has requirements in order to participate in a class, Dance Studio Manager makes it possible limit registration until the prerequisite is completed. In the online client, if the student has not taken enough of the prerequisite classes, they will not be able to register for that class. And if an admin or teacher tries to register a student for a class, and they have not fulfilled the prerequisite, then they will be presented with a warning message before they are able to add the student to the class. 
(and also see the video at the end of this post!)

Enabling Prerequisites

To enable prerequisites, go to Settings > Global Settings, and search for “prerequisite”, and turn it on as shown below:

Requiring Prerequisites for a Class

From classes, go to the class that needs prerequisites, and edit Class Details, and then as shown below set to Required, and then add as many classes as you like using the Add button. The number to the right is the number of times they must have attended that class.

Video Explainer