I found this sentence in a short story:
「先生の口から『どうしたらいい』なんてセリフが出るとは意外でしたよ。僕はてっきり、子供たちには好きなようにさせてやりたいから、ほかの先生どもがぎゃあぎゃあ言ったときには、以前みたいに僕が子供たちをそそのかしたことにしてくれって頼まれるもんだと思っていました」
As far as I understand, the speaker - the viceprincipal of a school - due to a teacher complaining went to a classroom to check about an issue that teacher was having with the students, and found them with cactuses on their desk, to be studied as graduation project because they have supernatural abilities (「だって、サボテンには本当に超能力があるんです」).
I found that 「short past + ことにする」 means to act as something false were true, as confirmed also by this question; as far as I can tell, this is the translation:
It's unusual to hear a teacher say something like "What should I do?", right? Without doubt, since the kids want to people letting them [させてやりたい] do what they like, when the other teachers were complaining, I thought they were asking me to act for their sake [てくれ] as if I insigated the kids like before
but I'm not really sure, since it sounds odd, and I have some doubts:
以前みたいに means "like before", like he already did something like that before? Alternatively it could mean "previously" as in the viceprincipal did that before the students brought the cactuses, but if that's the case I don't understand why the 「みたい」.
what about もんだ? I know it's used, after the dictionary form of a verb, to state something that's expected or a social norm; does it mean the other teachers are asking that like it was something expected from the viceprincipal?
is my understanding of 「そそのかしたことにする」 right? I can only think, if my translation is right, that the other teachers want the viceprincipal to act like the cactuses were an idea he gave to the studends, like to cover the fact that it was something the students want themselves to do, but I'm not really sure about this.