Six children were taken to hospital and others had to be treated by paramedics after eating cakes laced with cannabis at a school.
The pupils, all aged 14, were taken ill at Denefield School in Tilehurst, near Reading, on Friday.
A student had taken the cakes onto the school premises and handed them to a “small number of friends”, West Berkshire Council said.
It added a pupil had been permanently excluded as a result of the incident.
The local authority said the students were treated at the school’s first aid facility and then by paramedics before six of them were “admitted to hospital as a precaution”.
It said the “adulterated” baked goods had contained “cannabis or a cannabis-related product” and the incident had left the secondary school’s staff “deeply concerned by this isolated and unprecedented incident”.
‘Committed to student welfare’
The council said it was possible more students would be excluded and the matter had been referred to the police.
A spokesman said: “The school has an extremely robust drugs policy and takes drugs education very seriously.
“The school’s trustees, the headteacher and the whole school staff are absolutely committed to the safety and welfare of students.”
Dominic Boeck, West Berkshire’s councillor for education, said staff did “everything they should in response” to the incident and added there was “little they could have done to prevent it happening”.
“It’s an important lesson to learn that we need to continue driving the message to young people that drug and alcohol abuse is a significant threat to all of us,” he said.
Headteacher Edwin Towill told the BBC he was meeting parents on Monday evening and would speak publicly on Tuesday.