Thank you for specifying. As a workaround we can suggest using only one custom multivalued attribute. In each attribute item value you can specify the name of a school and the name of a class. Alternatively, you can use custom text attributes and specify classes as separate lines. It will look like the following:
For us to provide you with detailed instructions, please, specify which approach meets your needs and post here or send us (support[at]adaxes.com) a screenshot of the Scheduled Task currently used to populate class names. If there are PowerShell scripts executed, please, post here or send us the scripts in TXT format as well.