This is the first I’m hearing about models trained on real CSAM.

Give link or cry.

What are they to stop?

I recognize that others have filled the void and answered, but to answer you: what are they to stop?

Not finishing your sentence is almost as great a sin.

Don't be so sure. Google has shown in the past that they store information typed into search bars even if the user does not commit the search.

In your mind you have already been targetted by having your image somewhere you don't want it.

Start by DMing the schools account and request that the following images be removed because they contain your likeness. Link the photos.

The school doesn't need to make a big stink or even ask you why you don't want to be seen online, it's literally none of their business.

Whether they choose to respect your privacy is another story.

Should they fail to remove the photos, move on:

Contact the school administration office and ask that you would like to make a complaint about images posted on the Schools Instagram Account. When they ask why, explain that you would like x number of images removed because they contain your likeness. If they ask why further, explain that you do not want images of yourself online that you yourself do not control. End of story.

They can agree, or not, but I'm sure this would be better than going legal on them.