It wasn't that different from anywhere else: a mix of math, science, literature, history, geography and languages. English and German were often offered as languages, depending on the school.

Pre-revolution history wasn't changed all that much, except that the czars were viewed as decadent and corrupt and the achievements which are usually ascribed to the ruling class were considered to belong to "the Soviet people" in general. Revolution and post-revolution history, on the other hand, was full of communist propaganda, and propaganda pieces occasionally turned up in literature class as well.

The occupation of the Caucasus wasn't exactly seen as controversial until the recent wars in Chechnya. The subjugation of the Caucasian tribes was never questioned by most of the country. Although the Caucasian peoples themselves probably disagreed, they were isolated to a small part of the country, so their perspective wasn't heard by most Soviet citizens. They would also be punished by the government for any attempts to express ideas of independence. As for the Circassian genocide, it wasn't and still isn't covered in school curriculum. The majority of Russians have probably never even heard of such a thing, and those that have might not view it as genocide.

School curriculum didn't change much during the Soviet Union's existence, except that the propaganda gradually became more toned down and less nauseatingly slavish to the party leaders after about 1960.

This isn't based off of any historical source, just the combined accounts of various family members who were born and educated in the Soviet Union.