The Knuckleheads (ボンクラーズ Bonkurāzu) is a group consisting of Tomo Takino, Ayumu "Osaka" Kasuga and Kagura. Out of the six main characters from the series, the three of them are the dumbest, or those who get the worst results on exams. The "group" is first mentioned when Kagura is introduced to the class, and finds that nearly everyone is smarter than her, with an exception for Tomo and Osaka, in whom she finds her "equals".
The trio being called the "Knuckleheads" (also "Bonklers", "Boneheads" or "Numbnuts" depending on translation) started when Kagura called Tomo and Osaka "Bonkurāzu", however, Osaka did not initially believe this included her because she thought Kagura had only been speaking to Tomo and saying "Bonkura" which is singular.
- To Yukari's surprise, all of them managed to make it into college.
- They were the only three out of the main girls who had never been on a plane before the class trip to Okinawa.
- Once, their exam results were 30 (Kagura), 31 (Tomo) and 42 (Osaka), making their combined score 103 points. They compared themselves to Chiyo, whose score was 100 points, exclaiming "The Knuckleheads win!! We're not knuckleheads!!"
- They are all about the same height and have similar hair colours.
- When appearing together, Tomo and Kagura usually have angry expressions on their face, while Osaka maintains the same smile she usually has, but with similar yet smaller eyes.