It's really a very juvenile prank, replacing all of his notebooks with sparkly girly ones on the first day of school. And a lot of effort for the expected effect? Like this is a lot of notebooks. Are they just expecting him to spend the whole morning not using any notebooks and then shake them down at lunch or something? Fuck that noise. His masculinity isn't that easily threatened, and besides, these are some high quality notebooks.
Those thoughts take about five seconds to go through his head and cause a single mildly exasperated sigh, but after that he just grabs one of the notebooks at random for the first class of the morning, places it in his bag as if absolutely nothing is wrong, and goes to Geometry. He's certain he can hear some giggles nearby but since he's also certain of who did this he doesn't try to look for the culprit.
When he gets to his seat in class and has to grab his notebook, he locks eyes with Joshua with the most impassive look in his face, opens it, and starts nonchalantly writing the title of the class at the top. Joshua goes from smirking to uncertain to uncomfortable to deciding that maybe he should start paying attention in class too, which is good enough for Peter, and more than worth the probably horrendous scribble he ended up writing. His handwriting isn't great at the best of times but not looking at the paper while writing on it is bound to cause something nearly illegible.
With another sigh he looks down at the page, already grabbing his Wite-Out pen to erase and rewrite the word "Geometry".