A teacher has been suspended following claims that tape was put over the mouths of several pupils.
Parents and pupils said a teacher at Danesfield School in Williton, Somerset, lined the students up for being noisy before applying the tape.
The school said it took "all allegations concerning the welfare of our children very seriously".
Avon and Somerset Police said it was aware of the matter while the school said it was "thoroughly investigating".
A school spokesman added that "a member of staff has been suspended whilst the investigation continues".
"My thanks to the numerous parents who brought this matter to my attention and have given their ongoing support to us in this challenging situation," said head teacher Ian Bradbury.
One of the pupils said the teacher used the tape "because we were talking", while another described being lined up to have their mouths taped.
"Some people got really bad rashes and this girl in my class had her lips bleeding," one pupil said.
Parent Rob Lovell said his 10-year-old daughter was "shocked" by what happened and that the tape had hurt her.
"When she removed it at the end of the lesson it took the skin off her lips and made her lips bleed," Mr Lovell said.
"She was a bit upset telling us because she thought she'd done something wrong."
Mr Lovell said his daughter had told him that most of the class had tape put on their mouths apart from "maybe two" who were allergic.
"She said if they took it off they'd be taken out of the lesson," he added.
"When the Sellotape started to come off she put more on. She got them to keep it on for the whole lesson."
Another parent, Stacey Bradbury, said her 10-year-old son was "very, very upset" over the incident.
She added she was "disgusted and shocked" after the teacher apparently lined the pupils up and "one-by-one Sellotaped their mouths".
Danesfield School converted to an academy at the beginning of the month.