A 16-year-old St. Paul boy pleaded guilty Friday in juvenile court to injuring a Central High School teacher and an assistant principal in a case that has reignited teachers’ complaints about school discipline.

The teen pleaded to felony third-degree assault, plus two gross misdemeanors of fourth-degree assault and obstruction of legal process. He will be back in Ramsey County Juvenile Court for disposition — sentencing — on Jan 5. He was released to his parents and placed under house arrest.

While admitting to striking out at the teacher — and acknowledging that he caused the teacher’s injuries — the 16-year-old told his attorney in court Friday that he did not remember choking the teacher or slamming him into a table.

The teacher was hospitalized with a concussion, and an assistant principal had a bruised neck after trying to break up a lunchtime fight two weeks ago between two boys — a senior and a freshman. The 16-year-old, who is the older brother of the freshman, became incensed at the senior for fighting his brother. The Star Tribune generally does not identify teens charged in juvenile court.

The 55-year-old teacher intervened. According to court documents, the 16-year-old picked up the teacher and slammed him into a table and chair before slamming him to the floor. The teacher passed out for 10 to 20 seconds. He still suffers from headaches and vision problems, according to his attorney.

The teen also is accused of pushing an assistant principal into a wall, leaving that man with a “grapefruit-size bruise on his neck.”

After watching a cellphone video taken by another student of him assaulting the teacher, the boy said he did not remember doing the things he saw, his attorney, Diane Dodd, said after the hearing.

“I think the level of emotion and adrenaline make it impossible for your brain to comprehend everything that is happening,” Dodd said. “At the time, he saw someone punching his brother. And that’s all he was focused on.”

Jill Fedje, assistant Ramsey County attorney, was skeptical of the teen’s version of events, calling it “selective memory.” She added: “He remembers pushing him, but not choking him? OK.”

The younger brother also is accused of assaulting staff members and the assistant principal, allegedly punching “him repeatedly in the upper chest.” After the hearing, the teen’s parents left the courtroom without commenting.

The incident has sparked an uproar among teachers. Days after the assault, the St. Paul Federation of Teachers informed the School District that it was filing a petition for state mediation — a required step toward a potential strike.

“This was the breaking point. Teachers are asking, ‘What’s the union’s reaction to this? What are we going to do to make sure our students, teachers and support staff feel safe in school?’ This will force the district to come to the negotiations table,” Denise Rodriguez, the union president, said at the time.