In the school's newsletter, released today, principal Steve Hall said staff had been investigating an incident at Participation Day, an annual house competition day.
Mr Hall said as a result, 20 senior students were stood down for one day.
"As a principal and a school we are very disappointed. Many people work very hard for our students and the school, and this feels very disrespectful of that.
"However, our position on alcohol at school is clear and our thorough investigation, which has taken some time, revealed that some students had contravened that position and we have been consistent and fair in
our response.''
He said the students had made a "bad decision''.
''They have been remorseful and apologetic, and acknowledged that they have done the wrong thing.
''We look forward to learning and moving on from this.''
