Though Nick looks exactly the same on the outside, his experience with "frindle" makes him fear his big ideas a little bit. When he learns that people who buy things are called consumers and that consumers can put stores and restaurants out of business by not buying things, he immediately thinks of the horrendous food at the school cafeteria. He reasons that the students are all consumers and the cafeteria is a restaurant of sorts, and comes up with a plan to encourage kids to bring lunches from home until the quality of food improves at the cafeteria.
Nick's experience with organizing protests and making things change allows him to come up with other ways he can affect change in his community. This shows that Nick learned a valuable lesson about how protests and organization work in the real world. This is something that Nick will continue to be able to use long after he's no longer a student, which reinforces Frindle's role as a novel that models political protest.
However, Nick remembers what happened with "frindle," and he fears that people will figure out that it was his idea to boycott the cafeteria food. He thinks that anything could happen and worries about getting in trouble, so he doesn't tell anyone about his idea. Mrs. Allen notices Nick looking sad and down, but he tells her that everything is fine. Mrs. Granger notices the change in Nick too. She thinks that Nick is now quiet, careful, and doesn't laugh or joke with his friends anymore.
Nick's fear of what might happen implies that his brush with celebrity wasn't an entirely good thing, as he seems unable to consider that his celebrity might actually be able to help him in this endeavor. This suggests that Nick may have learned an incomplete lesson on what celebrity is and can do, as it is possible to embrace the power of celebrity and use it for good.
Near the end of the school year, Nick remembers the letter that Mrs. Granger wrote. He figures that she forgot about it since she never gave it to him, and he's too afraid to bring it up. On the last day of school, he works up his nerve and goes to talk to Mrs. Granger after seventh period. She's happy to see him and says that his visit will save her from having to mail him a letter later. When Nick says he came for the letter, Mrs. Granger reminds him that she promised he'd get it when the whole thing is over—and it's not over. She says that Nick will know when it's over.
The insistence that the conflict isn't over is confusing for Nick, but remember that Mrs. Granger is only positioning herself as the bad guy to make sure that "frindle" makes it into the dictionary. This suggests that Nick isn't fully aware of what he's done with "frindle," as it never occurs to him that it might one day become a real word in the dictionary.
Mrs. Granger approaches Nick. They're almost the same height, and Nick notices that her eyes are soft but still powerful. She remarks that she's noticed how quiet Nick has been and tells him that he didn't do anything wrong. Mrs. Granger says that his idea was a good one, and she's been generally proud of the way that he handled everything. She tells Nick that he'll go on to do great things, and he shouldn't let a few difficult days slow him down. She shakes Nick's hand, looks him straight in the eye, and tells him to have a good summer. As Nick leaves, he wishes Mrs. Granger a good summer and reminds her to buy new frindles for next year.
Mrs. Granger's pep talk makes it so that if Nick were to think about it, he might realize that she actually supported "frindle" and just fought him on it to teach him how exactly to stand up to authority figures. Especially when she speaks to him as more of an equal than an authority figure, she makes it clear to him that there's not actually anything wrong with standing up for himself and for what he believes in.
Because of Mrs. Granger's talk, Nick is able to find pride in what he did with "frindle." He enjoys thinking about the commotion he caused and as he progresses through school, he continues to have big ideas. In seventh grade, his big idea to improve the cafeteria food results in delicious meals and a visit from the state superintendent, who is interested to learn why Westfield has the most successful lunch program in the state. The narrator explains that Nick did many more things, but the end of this particular story about Nick takes place ten years later. During those ten years, "frindle" becomes a real word.
Again, when Nick is able to put what he learned into practice and improve the cafeteria lunch program, it models how the lessons of Frindle can be expanded upon and used in the real world to change other things. This also suggests that Nick accepted that he can use his celebrity and his leadership role for good, and that he can use his privilege to help these changes along.