Federal Title IX law prohibits schools that receive federal funding from discriminating based on sex, which includes pregnancy and related conditions (such as breast/chestfeeding).
The Illinois Human Rights Act protects any person from being denied enrollment or full and equal access to facilities or services at any place of education (including elementary, secondary, undergraduate, and postgraduate schools) just because they are breast/chestfeeding or needs to pump milk.
*Chestfeeding is an alternate term for lactating people that do not to use the term “breast” when referring to their bodies.