How is the title of The Wednesday Wars significant to the plot?

The title of the book is significant to the story because it references what has to happen to Holling Hoodhood every Wednesday afternoon.  
Holling is a Protestant. That's important because he is the only Protestant who attends his school. Everybody else is either Catholic or Jewish. On Wednesday afternoons, all the Catholic students go to Catechism, and all the Jewish students go to Hebrew studies. The administration has to figure out something to do with Holling. Their solution is to put him in a study hall-type class with Mrs. Baker.  
Mrs. Baker is not happy about the situation, and she initially makes Holling do menial tasks like clean desks and chalkboards. Holling doesn't enjoy it, and he believes Mrs. Baker hates his guts. After about a month, Mrs. Baker decides to use the time with Holling to teach him Shakespeare and have him read a play per month. Holling thinks that's just about the worst thing possible. He feels Wednesdays are essentially a battle between him and Mrs. Baker, hence the title The Wednesday Wars. As the novel progresses, Holling and Mrs. Baker grow to enjoy their time together.