Three boys have been expelled from a top private school in west London and a fourth has been suspended after cocaine was found at a school dance.
The class A drug was discovered at Latymer Upper School's end-of-year prom at Bush Hall in Shepherds Bush in May.
Head Peter Winter said the expelled boys have been allowed to return to school to take their A-level exams.
The drugs were found as two of the boys were stopped by a security guard in a toilet during the event.
The £4,800-a-term school, founded in 1624, counts actors Hugh Grant and Alan Rickman as former pupils.
The sixth-formers are sitting papers in a different room to other students, Mr Winter said.
He added: "The four boys had different roles in conspiring to procure some cocaine, and one of them was discovered with it on him.
"They were planning to take it at a club after the event.
"Three of the sixth-formers - their parents were asked to withdraw them, and they did. The fourth was suspended at the end of term."
He added that he allowed the expelled boys to take their A-levels as "I am not in the business of ruining kids' chances in the future by not allowing them to take their exams".
The school head has written to parents about the incident adding that a "small number" of students had been drinking prior to the dance.
Mr Winter added that he had not contacted the police about the incident.