Yuuji and Yoshiithrowing the test papers from the roof of the school, forcing the teachers to prepare a new test and nullifying Nemoto's attempt at cheating.
In episode 11, Yuuji, Yoshii, Voyeur, and Tetsujin each have a CMOA. Yuuji's is for intentionally letting his grades fall until the very last test to throw off their opponents for the ESB, then letting the poor grades become known to their opponents so he could surprise them by overpowering Class D's summoned beings. Yoshii had his summoned being punch right through a wall dividing the classrooms, even though his own bones began to crack and his knuckles bled, but even that turned out to be a decoy for Voyeur and Tetsujin to get their CMOA, as Voyeur crashes through the window with Tetsujin to set up a surprise battle in health to finish off the Class B rep.
Yuuji gets an awesome one defending Shouko after a couple insults her publicly about her dream to be a bride in episode 7 of Season 1.
Class F almost defeating Class A's superior academic strength with clever tactics near the end of the first season. They could've easily won the battle had Yoshii's Iron Bracelet not died at a crucial moment.
Akihisa had a Crowning Moment of Heartwarming with Minami during Episode 8 of Season 2. On Yuuji and Akihisa's side however it becomes a Crowning Moment Of Awesome, as told on the light novels. When Minami's Classics textbook got messed, Yuuji and Akihisa did their best to replace it, including riding downhill with both of them in the same bike just to chase the container van which had the school's extra supply of books taken away. Counts as Establishing Character Moment for both Yuuji and Akihisa's... uhh... weird friendship.
Akihisa doing a Big Damn Heroes moment in Volume 9 of the light novels. He went in late due to a... uhh... certain incident, but by the time he arrived, 2-F was already cornered into submission on their war with 2-C. With the help of 2-A, he got behind enemy lines to cut through to where Mizuki was, who was about to be victimized by 2-C and 2-B's plan to disqualify her from the ongoing war, which will cripple class 2-F's chances of winning. He gets there on time, completely destroys their enemies' elaborate plan, which also involved a subverted Red Herring war against 2-A and 2-B, and Mizuki and Yuuji proceeded to finish the summoning war via a Curb-Stomp Battle.
Of course, Yuuji and Yoshii's final battle of the summer OVA competition counts. After purposely getting hurt, Yoshii turns a losing battle around by letting his opponent block his teammate's shot for him. This leads to that guy getting knocked out and Yoshii's avatar unleashing a Limit Break that warps the battlefield and deliver a No-Holds-Barred Beatdown to the last guy.