A bomb was let off at the arena at the end of an Ariana Grande concert on Monday night (May 22).
At least 22 people have died and a further 59 were injured in the blast.
Helsby High released a statement which said 'a number' of students were at the gig, but they had not heard about any being physically injured.
The school added help was available for teenagers dealing with the traumatic after effects of going through 'a very difficult experience'.
Headteacher John Dowler said: "The school is shocked and saddened by the events that happened at the end of the Ariana Grande concert last night.
"Our thoughts are very much with the families and friends of those who have suffered loss or injury in what appears to be a suicide bomb attack."
Thousands of fans had travelled to the arena from across the country to see the American popstar.
Mr Dowler said: "I know how many parents and staff will have waited in the vicinity of the foyer of the Manchester Arena to collect their sons and daughters.
"We are aware that there were a number of our students at the concert last night and we are relieved that to date, we have not been informed that any of them have been physically hurt.
"However, we are aware that they will have gone through a very difficult experience and staff are being watchful today and support is available in school for any who require it."
Parents and guardians who are concerned about their child should contact Helsby High through the relevant year group email.
Greater Manchester Police have also set up a helpline on 0800 096 0095 for anyone worried about missing family or friends.