One week has passed since he was assaulted by a group of men and sustained serious injuries to his arm, but Chattraphat Namjundee, a 26-year-old PE teacher at Mathayomwatsing School in Bangkok's Bang Khunthian district, is still in a state of shock over the attack.

"I was punched, kicked and hit with a chair and table by a group of men I have never met before. I had to run for my life and lock myself inside a room until police arrived," he recalled.

Mr Chattraphat was among 12 people injured last week when a group of 24 men stormed Mathayomwatsing School, where 248 high school students were taking their GAT and PAT exams, disrupted the tests, vandalised property and attacked security guards, the school director, teachers and students.

The intrusion took place after the school asked people at an ordination ceremony at neighbouring Wat Sing to turn down their loudspeakers so as not to disturb the students.

"I was supervising the tests when I heard screaming from lower floors. I realised there must be something wrong so I went out to look and saw a female teacher being slapped by the assailants. I tried to stop them and calm them down, but they got mad and started attacking me, so I told the students to flee to safety," Mr Chattraphat said.

Reports of the events that day drew outrage from the public. Prime Minister Prayut Chan-o-cha joined the public in condemning the incident and said the men would be dealt with urgently.

The next day, 24 men aged 18 to 41 turned themselves in to authorities. They were charged with invasion, property damage and assault. Sixteen of them had been prosecuted for drug abuse in the past, although none tested positive for drugs in this case.

One suspect was also charged with sexually harassing a minor after a student claimed she was molested while trying to break up a fight between the attackers and her friend.

After being hailed as a hero for protecting his students, Mr Chattraphat said he was only doing his job, and behaved as any good teacher would in the circumstances.

"I care deeply for my students and their well-being. That is why I did what I did that day," he said.