Pupils in Ringmer were met by drug sniffer dogs checking for cannabis as they arrived for college.
Ringmer Community College invited the Sussex Police passive drugs dog team to make checks to identify any pupil taking the drug into school.
The dogs, accompanied by uniformed and plain-clothes officers, checked pupils as they entered the college.
No arrests were made.
The operation was one of several recently organised across Sussex.
College principal Steve Johnson said: "Sadly in all secondary schools now, there are pupils who are tempted to bring cannabis on to the site.
"We aim to do everything possible to prevent this and are determined to identify anyone involved."
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