The West Swindon Neighbourhood Police Team (NPT) used a passive drugs dog to monitor pupils going into Lydiard Park Academy, Swindon, on the morning of Monday 8 July.
The dog indicated that three pupils might be in possession of drugs. They were then searched by police officers. No drugs were found however they admitted being around someone who had recently used illegal drugs.
Temporary Police Sergeant Pete Foster of the Swindon West and North Central NPT said: "The use of illegal drugs is a major cause of anti social behaviour and is often funded by theft related crime and it is one of our local priorities to stamp this out.
"The operation was run with the support of the school who we work closely in partnership with in such matters.
"I see it as a positive result that no drugs were found, indicating that illegal drugs are not being taken on to school grounds."
If anyone has information regarding illegal drug activity they should contact the West Swindon Team via 101 or Crimestoppers on 0800 555 111 where information can be left anonymously.