You can create a discount that will only be valid for specific groups of classes or students, but it's easy to configure these types of discounts incorrectly! Let's take a look at the right way to set one of these types of discounts up.
Discounts for groups of classes
Let's say you want to create a discount that will only be valid for all of your painting classes. You might think you would do so by selecting "Class" from the "What items should the discount apply to?" menu, and then adding all of your painting classes to your rule.
However, by selecting Class and then adding multiple classes to your rule, what you are really saying is "ALL of these classes must be in the student's shopping cart in order for this discount to be valid."
If what you actually want is for the discount to be valid if ANY of those classes are in the student's shopping cart, what you need to do is select "Course Group" instead of "Class", and then add the course group containing the classes you wish to make discountable to your rule.
If not all of the classes you want to target are in the same course group, or if you don't want to discount all classes in a particular course group, you can create a new course group just for the purpose of your discount. Just make sure you uncheck "Show Online" when you create the course so the course group doesn't appear in the navigation of your online registration site.
Discounts for groups of students
The same thing applies to discounts that should be valid for a group of students, except instead of creating a course group to point to, you'll create a customer group and point to that instead.
In this example, any student in the customer group "Art Students" will receive this discount.