Three pupils were rushed to hospital when they “reported feeling unwell” after eating cannabis cakes at school.
A 16-year-old girl baked the brownies at home before taking them to Shirley High School in Croydon, south London and shared them among a group of six, according to the Sun.
Teachers called emergency services at around 3pm on Friday March 29 after a number of students fell ill.
The Sun reported that police officers had spoke to the girl, but she is unlikely to be expelled.
A Metropolitan Police spokeswoman said: “Police were called at 14.56hrs on 29 March to a school in Shirley Church Road, Croydon, after a number of students reported feeling unwell.
“Officers attended with LAS (London Ambulance Service).
“Three pupils have been taken to hospital. None are in life-threatening condition.”
The force has made no arrests but said it was “working to trace a number of other pupils”.
Shirley High School Performing Arts College was not immediately available for comment.
The comprehensive school has just over 1,000 students and first opened in 1954, according to its website.