Reports of a person with a knife inside the grounds of Barton Peveril College following an incident last week were started by a student.
Police were called to the College in Eastleigh on March 9th after reports of someone with a knife inside the grounds.
The college was placed in lockdown with students told to stay inside.
Some hid in cupboards while others hid under desks, as police dealt with the situation.
Hampshire Police said three boys suffered minor injuries after being assaulted by a group of five or six boys who had entered the school grounds but no knife injuries were suffered.
Officers say it was an isolated incident and no weapon has been located as investigations continue.
The sixth form says staff will be checking students' ID before they're allowed onto campus and has sent a letter to reassure parents and guardians.
The college says it is currently working closely with police to establish the exact nature of the disturbance.
In a statement from the college, Principle Rob Temple said: "The rumour of a knife...would appear to have started with a student (who has since admitted that they had not actually seen a knife) which spread across the student body and was then reported to me by several members of staff as "a masked intruder currently on site with a weapon."
"The lockdown lasted approximately 35 minutes, finishing when the police declared the site safe, after which we returned to normal lessons.
"It transpires that there had been a group of unauthorised persons who had briefly gained access to the College site about 45 minutes previously.
"It would appear that they targeted an individual, and also hurt a bystander, both of whom suffered minor injuries, and the left- pursued by a group of our students (including the victim).
"We have since reviewed CCTV footage (of which there is plenty) and we can confirm that there is no evidence of a knife at any point in the incident.
"The police have the names of the intruders (none of whom were Barton students) and one of them has been arrested and charged.
"I am also in ongoing discussions with local schools and colleges to ensure we are sharing information and coordinating our response to the incident and any future concerns.
"As a result, two students have since been permanently excluded from the College.