The word harassment is misspelled on the chalkboard during the meeting-it is written there as "harrassment".
When Ned Flanders introduces himself to the class, he says "So, rub a dub dub, 30 kids and their sub!" There are 5 columns of desks, 4 deep, so 20 students. "20" would have fit in to his rhyme just as well as "30".