But, more worryingly, one of the youths caught in the act by CCTV cameras was seriously injured and blood is clearly seen dripping from an injury to his hand or arm. What may have been a nasty prank ended in serious injury and could easily have resulted in a death.

John Platt, principal of the school, is deeply worried about the development. He told the Times: "Two young boys smashed a window to break into the school at about 10.40pm on Saturday evening and they were caught on CCTV.

"It was very worrying to see the younger of them badly cut when he slipped coming through the broken window. On the CCTV you could see the blood flying from his hand. He was obviously very seriously hurt.

"You could see that he was in shock and the other youth, who seemed to be dominating him, didn't seem to have any compassion or to be doing anything to help him. The younger boy was so out of it he even took his hood down.

"In the end they took a computer monitor and caused some damage but there was blood all over the place. I am really concerned for the young boy's welfare.
"I would be worried if I was his parent, he obviously needs medical treatment. I would advise his parents to hand him over to the police and start sorting out his behaviour. He needs help."

Mr Platt has revealed that a new CCTV system has been put in place at the school and is connected to a monitoring station and the police. He said: "We have had five break-ins in the last two-and-a half months. We thought there might be a pattern emerging but this latest incident seems to be more coincidental.

"The two young thugs were distinctive, one about 14, the other about 16-years-old. The police are investigating but it is a real hassle for the staff and the pupils when something like this happens."

Police said: "We can confirm that a school at Greenaway Drive in the Millburn area of Coleraine has been broken into. The burglary was discovered sometime over the weekend.

"Anyone who noticed any suspicious activity in the school grounds is asked to contact the police at Coleraine. The telephone number to ring is 0845 600 8000, or contact the 'Crimestoppers' charity anonymously on freephone 0800 555111."