You are right that Calpurnia provides a quick lesson in proper behavior at the supper table in Chapter 3. She scolds Scout and tells her the way she is speaking to her "guest" is inappropriate.
But the fact is, Scout is learning about "proper behavior" throughout the book, from almost every character. Whether the lessons are direct or indirect, each character she interacts with provides a model of proper or improper behavior.
In chapter one, her brother Jem's easy way with meeting Dill and forming a friendship is a social lesson for his younger sister. She looks up to Jem.
Miss Caroline, in chapter two, also gives Scout a lesson in "proper behavior" for a traditional classroom. This is a lesson Scout neither understands nor agrees with. As a result, Atticus finishes this lesson on the porch in chapter 3, and teaches her the infamous lesson of considering other people's feelings.
I encourage you to read each chapter with the idea in mind that each situation Scout encounters is a potential "life lesson" or "behavioral lesson." It will help you understand some of the deeper themes of the book, as well as track Scout's growth and maturity.