You can "block" clients from taking certain classes based on tags in the Service type. This is a great way to drive clients towards a consultation or intro class, prior to them taking more advanced classes or signing up for your studio!
How to set up booking restrictions:
Go to Set up > Service Types
Here's the page on setting up a new Service Type
On the last step, under "Advanced" you will scroll down to Booking Restrictions
Add in the tags attached to clients that you would like to be able to access this class
For example, if you have a tag that is associated to all Advanced Pilates clients, then you would enter in that tag into the "Booking Restrictions". This would mean that any clients with the Advanced tag would be able to book that Service Type!