Mrs. Blount, the 6th grade teacher at Scout’s school, is a veteran teacher. When the newcomer, Miss Caroline, comes to the school straight out of college (and as an outsider in the Maycomb community), Mrs. Blount probably doesn’t have much faith in Miss Caroline’s abilities. When Miss Caroline’s class begins to get a little rowdy over Scout’s seemingly disrespectful behavior, Mrs. Blount chastises Miss Caroline about the noise they are making. She says that their noise and laughter is disrupting her class from learning. Mrs. Blount is also probably suspicious of Miss Caroline because she teaches the Dewey Decimal System, a new educational strategy at that time. 

Overall, Mrs. Blount is not too welcoming to the new teacher, Miss Caroline, and like Scout, probably doesn’t care for her new learning techniques and ignorance as to how to teach children in Maycomb.

The answer to this can be found in Chapter 2.

Mrs. Blount is the sixth grade teacher at the school that Jem and Scout attend.  Miss Caroline is the first grade teacher.  She is new at the school and has new ideas about education.

In Chapter 2, the class starts laughing at Scout (and I think perhaps at Miss Caroline) when Scout is "whipped" by the teacher.  They apparently laugh pretty loudly.

This is what makes Mrs. Blount angry.  She says that her class cannot concentrate on their work when the first grade is making so much noise.