Hi Jillian,
Within the discount code settings, you should see the option to add an advanced filter (towards the bottom). You should be able to select Class Year under the custom contact field section, and then set the operator to "equals" and select 2020 as the choice. As long as you have the discount to automatically apply, it should only do so to those who select 2020 as their class year.
Thank you!
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Erica Kennedy
Principal Client Success Manager
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