Hi , @dylandavis09
According to your description, you want to find the student names displayed based on the selected grade level.
Here are the steps you can refer to :
(1)This is my test data:

(2)We can use this code in the "Full Name" Combo box -Items to filter the FullName table:
Filter('Choices Test', 'L-Grade'.Value = ComboBox1.Selected.Value).'Full Name'
If you want to multiple selection you can also use this :
Filter('Choices Test', 'L-Grade'.Value in ComboBox1.Selected.Value).'Full Name'
However, this does not support delegation, and you can decide whether you need it based on your actual usage.
The 'Choices Test' is my SharePoint list name , you need to replace it in your side .

The result is as follows:

Best Regards,
Yueyun Zhang