Tom wishes he were sick when he wakes up on a Monday morning and contemplates a whole five days of sitting still in school ahead of him:
Monday morning found Tom Sawyer miserable. Monday morning always found him so—because it began another week’s slow suffering in school. He generally began that day with wishing he had had no intervening holiday, it made the going into captivity and fetters again so much more odious.
Tom, of all people, loves being active. Also, the school master he has to face is not the kindest person in the world.
Tom has a loose tooth but he knows that won't work, as Aunt Polly will simply pull it. Therefore, he moans and groans and says he has a sore toe, but that doesn't work either. Aunt Polly sees through his stratagem, and, unfortunately for Tom, he lets slip that he has a loose tooth, so she pulls that as well.
Tom does end up late to school. He is going to lie about it, but sees a beautiful new girl sitting in the schoolroom. He doesn't want to lie in front of her, so he tells the truth. This earns him a whipping from the schoolmaster.