Three schoolchildren were taken to hospital after they were poisoned when a pupil allegedly added a coloured chemical to their water bottles.
A pupil and a group of their classmates at the Oxfordshire school are reported to have deliberately put copper sulphate in the water after they were drawn to the colour of the compound, which turns water bright blue, during a science lesson.
Three pupils at Lord Williams’s School in Thame were taken to hospital last week.
Ingestion of copper sulphate irritates the digestive system and may cause sickness, which may limit its poisonous effects, according to the US National Pesticide Information Centre.
But symptoms of consuming it would include nausea, vomiting, diarrhoea and upper abdominal pain.
The compound is a fungicide and herbicide used to kill fungi and bacteria in crops and to kill algae in water.
All three children later returned home, according to the Oxford Mail.
Headteacher Neil Dimbleby told the newspaper on Monday: “Three students stayed in hospital overnight having ingested diluted copper sulphate that had been taken from a laboratory.
“The police were informed and have been supporting us through this incident.
“We are pleased to report that the students are all now safely at home.”
A parent of a pupil at the school is reported to have contacted the police following the incident.
No one from Thames Valley Police was available to comment, when approached by The Independent on Monday.
Lord Williams’s School, a co-educational secondary school with academy status, has around 2,200 pupils.
The Independent has also contacted the school for comment.
