You can also perform special shows (including group sex stageplay) at the brothel on Fridays, and initiate gang bangs in math class....
Also, with max Exihitionism, you can initiate gangbang before the swimming lesson. Just strip naked, sneak out of your changing room and walk in to the other sex changing rooms. Just not through the swimming pool (as this will start the lesson), but through the school corridor entrance. If you goad the surprised classmates, 5 to 6 of them will fuck you, which will get your limbs and orifices busier than during a tentacle encouncer (outside of the Tentacle plains). No ear slime required and 100% consensual, so no trauma or stress and works everytime, unlike the maths or toilets events, which are random. The only downside is you'll earn delinquency twice, one for intrusion, second for being late for the lesson, plus a third for swimming naked in the school pool, if you wish to do so.
Strangely enough, you won't be able to initiate a gangbang this way after the swimming lesson, only seduce and fuck just one classmate, while the others watch and take photos. Guess they're too spent having swum in the same pool with you practicing your backdoor stroke.
I've been thinking that perhaps these evens in school could be not the PCs own ideas, but something suggested by other NPCs. I see a corruptive plotline with the School principal, where they either blackmail you into such acts of lewdity or the PC is having a perverted affair with them (which starts when the PC keeps going to detention to receive punishment even though they have struck a no more detention deal) and willingly performs more and more daring acts at their behest. It just feels too easy to achieve currently, there isn't even a seduction test in order to convince those 5-6 peers to gangbang you. Yet at the same time you need to succesfully seduce one to have a public sex with them after the swimming lessons. Which feels a little bit odd, don't you think? All you need is lv. 5 Exhib (which you can currently achieve in just 2-3 days and lv. 5 Promisc, which can also be achieved in a week's time if you start the game with a Promiscuous bonus and take up Measure genitalia as your school project to provide your PC with extra opportunities to raise your lewd stats, apart from whoring in the Brothel or servicing gloryholes. It's just a little bit too much too quick in my opinion, with this one ganbang repeatable event outpacing other lewd acts within the entire process of the PCs descent into depravity.
Other naughty acts requested by Leighton could be added, involving school cafeteria, library or playgrounds, so there would be more things to do at recess besides teasing Kylar, satisfying/avoiding Whitney, relaxing on a stump (this just begs for more stump relaxing techniques) or messing around in the Toilets.