A Challney High School for boys pupil is in hospital after an altercation at the school on Friday.
The 12-year-old pupil is believed to have undergone a five hour operation at the hospital last weekend.
Police were called to the school shortly after 2pm on May 1.
A spokesman for Bedfordshire Police said: “Police were called to reports of an altercation at Challney High School in Stoneygate Road at approximately 2.20pm on Friday, May 1.
“A 13-year-old boy from Luton was arrested on suspicion of causing grievous bodily harm.
“He has been released on bail until 18 June.
“A 12-year-old boy was taken to Addenbrooke’s Hospital where he remains at this time.”
A family friend of the injured boy, who does not wish to be named said: “The boy is a good kid, very quiet and well loved by everyone.
“The whole community is praying for his recovery.”
A Challney High School for boys spokesman confirmed a pupil is receiving hospital treatment following an alleged incident at the school.
He added: “We also called the police to report the incident and have been working with them to determine exactly what happened.
“Challney is a very happy and peaceful school community so we are all shocked and upset by what has taken place.
“All of our thoughts are with the boy and his family at this time and we have been in regular contact with them,” he added.