In The Wednesday Wars by Gary Schmidt, why does Holling believe that Mrs. Baker is plotting against him?

At first, Mrs. Baker seems very annoyed that Holling Hoodhood is the only student who does not attend Hebrew school or catechism on Wednesday afternoons, so she has to stay with him in the classroom. He believes that she is plotting against him (though she turns out to be a very supportive teacher) because she is angry that he has nowhere else to be on Wednesday afternoons.
At the beginning of the year, Mrs. Baker is very hard on Holling. She gives him the most difficult sentences to diagram. Everyone else in the class gets fairly easy sentences, while she gives him very complicated sentences with a great number of clauses. In addition, she is at times curt with him, such as when she tells him to go to the office, where he receives the news that Mrs. Baker wants him to re-take sixth-grade math. She also makes him carry out tedious chores, such as washing chalkboards and pounding erasers, and then she decides to make Holling read Shakespeare--which he considers torture. In the end, however, Holling realizes that Mrs. Baker is really his friend and is trying to encourage him to learn.