In the episode you are talking about, the teacher (Miss Gates) is talking about current events. Specifically, she is talking about the Nazi regime in Germany and what they are doing to Jews and other people they don't like (so Hitler is in power as leader of the Nazi Party).
What the teacher says is that there is prejudice in Germany, but there is none in the United States because the US is a democracy and Germany is a dictatorship.
This is hypocritical because of the way that the town has acted towards Tom Robinson. Their actions have clearly showed racial prejudice, but yet the teacher is talking about how bad it is for the Germans to be prejudiced. (In fact, Miss Gates herself said that the blacks needed to be taught a lesson.)
Miss Gates is Scout's third-grade teacher in chapter 26 of To Kill a Mockingbird. Cecil Jacobs shares a news article in class about Adolf Hitler and the treatment of Jews in Germany. A student asks Miss Gates how Hitler can treat the Jews so poorly, and she responds by telling the class that Hitler is the government in Germany since he is in power. She then teaches about the difference between a democracy and a dictatorship. The ironic and hypocritical comment from Miss Gates is as follows:
"Over here we don't believe in persecuting anybody. Persecution comes from people who are prejudiced" (245).
This comment is both ironic and hypocritical because many people in Maycomb are prejudiced against blacks. Many in Maycomb persecute blacks, too. Then, Miss Gates tells the class that she doesn't understand how Hitler could not like the Jews because they are great people. She concludes that Hitler must be against religion. However, she neglects to connect the situation in Germany with racism or the struggles of African Americans in the United States, which adds to the hypocrisy.