Toronto police have charged four students following a violent protest on Friday over recent expulsions at an east-end high school.

Hundreds of students joined the demonstration outside Birchmount Park Collegiate in Scarborough, angry that five of their peers were suspended for posting derogatory comments about their vice-principal on the popular networking website Facebook.com.

Several teenagers tussled with police officers during the rally and were arrested.

Police said there were a number of skirmishes, including one incident where a student allegedly swung his skateboard at an officer.

As the boy was being apprehended, another student grabbed the arresting officer, resulting in the second student being charged with obstructing a peace officer.

A third student allegedly tried to incite the crowd to use violence and cause damage. He was charged with causing a disturbance.

A fourth student allegedly threw a bottle at an officer, but did not cause injury. He was charged with assaulting a peace officer and assault with a weapon.

The four teens, three aged 16 and one aged 17, are to appear in court next week. They cannot be identified under the Youth Criminal Justice Act.

The protest initially drew only a few dozen students, but hundreds joined in when a fire alarm was maliciously pulled.

Several police cruisers arrived and officers closed off a section of Danforth Avenue.

The teenagers have said the punishment over "private" online comments violates their freedom of speech.

The student at the centre of the dispute is 16-year-old Brad Parsons, who set up the message board. Despite being under suspension, he joined the protest on Friday.

"I somewhat regret starting the group, but at another point I don't because it's freedom of speech, it's just us talking, and now look what's happened," Parsons said.

The teen is one of five students suspended in what the school board calls cyber bullying, to which it has a zero tolerance policy.

School board officials say more suspensions could come. The punishment in each case ranges from between five and 20 days.

One student posted comments Thursday night warning of a volatile demonstration.

"Be at the protest tomorrow, maaaaan, it's gonna be intense," the statement read.

An announcement inside the school said students who felt threatened by the violence could go home early.

With a report from CTV's Galit Solomon