What were roman teachers called at school?

There wasn't a single, universally used title for Roman school teachers. The title varied depending on the level of education and the social status of the teacher and students. Some possibilities include:

* Magister: This was a general term for teacher or master, applicable across a range of educational settings. It could refer to elementary school teachers (who taught literacy and basic skills) or more advanced tutors.

* Grammaticus: This title referred to teachers who instructed in grammar and literature, typically at a secondary level.

* Rhetor: This was a title for teachers who specialized in rhetoric and oratory, a higher level of education focusing on public speaking and persuasive argumentation.

So, there's no single "what were they called?" answer. The appropriate term depended on the context.