Appreciating what you have, not what you could have
At the start of the book, the students in Miss Nelson's class take her, and her kindness, for granted. They treat her badly, and frequently complain about her being a bad teacher. Likewise, they frequently throw paper airplanes and spitballs around the classroom. After Miss Nelson grows tired of this misbehavior, she concocts a plan to leave the kids in the hands of a cantankerous substitute teacher. After a short time with the substitute teacher, who is neither kind nor patient, the kids grow impatient and start to realize that they had taken Miss Nelson for granted. Because of their poor experience with the mean substitute teacher, they learn that Miss Nelson is a great teacher who cares deeply for her kids and their learning outcomes. They learn, in other words, to appreciate what they have.
The importance of discipline
One of the most significant themes in the book is the importance of discipline. After growing tired of her student's misbehavior, Miss Nelson disguises herself as a substitute teacher named Mrs. Swamp. In order to keep up the facade of Mrs. Swamp, whose personality is directly opposite Miss Nelson, Miss Nelson must remain incredibly disciplined to work against her nature and be rude, brash, and a disciplinarian. Her steadfastness in maintaining her facade shows the importance of discipline. By becoming Mrs. Swamp and acting like her so consistently, Miss Nelson demonstrates that discipline requires persistence, commitment, and the ability to put long-term goals above short-term comfort. Likewise, she resists the temptation to slip back into her kind and gentle nature because she understands that real change in her classroom will only come if she holds firm in her appearance and actions.
