Confusion surrounds the evacuation of Birley Academy, with neither the school nor South Yorkshire Police having released any details of the nature of the incident which sparked it yet.
Posting online, one parent said: "My son's just rang to say that there has been a drug search and that they are sending everyone home. What the hell is going on?"
Another suggested there had been a 'gas leak' and another said all pupils' bags were being checked for drugs.
A number of parents have said small groups of students have been escorted from the school by police officers.
One woman said: "I've just picked my son up. There's a lot of police and it's chaos. My son and his class were told to leave their bags and get out quick so half of the kids have not got phones or house keys."
A message sent to parents today said: "Unfortunately there has been an incident at school today and the building has been evacuated.
"It may be some time until we can return, students are being sent home. Please collect them from Birley Lane main entrance if you are able to. Please do not call school."