There are some instances in which a couple (a student and a teacher) is shown post-coital (no nudity).

There is a scene that heavily implies a man is performing oral sex on a younger man/teenager (the facial expressions of the teenager are shown, no explicit sex or nudity).

Rear male nudity of a particular character is shown several times.

Frontal nudity of the same character is briefly shown (the scene is dark and not easily visible).

There are a few instances where it is implied that a teacher and a student share a sexual relationship (no actual sex or nudity).

It is implied that a student is being sexually harassed (no actual sex or nudity).

There is some discussion between characters about different sex topics.

Kisses between a teacher and a student are shown.

A raven is electrocuted and killed.

The movie features strong, graphic brutal violence and gore, specially in the second half of the film.

It is implied a teenager kills his parents.

A man is hit hard on the head with an object and knocked unconscious. Later he is hanged.

A teenage girl is hit on the head with the same object, knocked unconscious and then thrown off the top of a building. The aftermath of the impact is shown.

A teenage boy slashes himself a few times. After, he stabs the tip of the knife on his back, and then he drives himself against a wall to bury the knife deeper into his back.

A teenage boy is burned on his face a few times with a hot welder by a man. Later the welder is buried deep into his cheek, killing him.

In the second part of the film several students are killed with a shotgun by a man. These instances are always explicit. There is a lot of blood and gore involved, and the impact of the bullets on the different parts of bodies is explicitly shown. Blood splattering is always present in these instances.

Towards the end, much of the school building is shown to be covered in blood, with the bodies of the students lying around everywhere.

A man sets another man on fire. The man is shown to be burning alive.

There is some profanity throughout the film.

S.O.B, s***, and f*** are said a few times, along with milder insults.

There is some smoking shown by a few characters.

A teacher invites a student to drink beer with him.

The film features brutal and disturbing violence throughout, more-so in the latter parts of the film.

Also, sexual relationships between teachers and teenage students are implied, once not-conscensual (more of it being thematic material, rather than frightening).