Ms. Zuckkus is Liam X, Ezzy X, and Stanley's former teacher (the one they had before transferring to Mrs. Husse's class). She's an ugly, cruel
teacher who verbally abused the three kids. Even after Liam X and his friends left her class, she continued to mess with them.
Unfortunately for Kate, she was in Ms. Zuckkus' class when she first moved to the city, and when the woman found out she was friends with Liam, she started being mean to Kate. Before Kate moved to Paris, Ms. Zuckkus and the principal held the others back a grade and put them in Zuckkus' class just to mess with them.