<p>I am sure Dean J will answer here when she has a moment however I imagine the decisions for EA are based on your sons academic results through the end of Junior year. UVA will then want to see his mid year report to make sure he is staying on track. They always have the option to rescind an acceptance if a students grades take a turn inconsistent with the results that the decision was made on. The same goes for any admit through the end of their high school career. 
Good Luck</p>