Pupils returning to a Kent school for the new term will be subject to random drug tests for the first time.
Mr Walker says 85% of parents have given permission for testing
In what is thought to be the first such scheme in a state school, pupils at The Abbey School in Faversham will have mouth swabs taken to detect drug use.
From Wednesday, 20 names each week will be selected by computer and the swabs sent off to a drug testing laboratory.
So far, 85% of parents have given permission for children to be tested, according to head teacher Peter Walker.
He said previous government attempts to prevent people taking drugs were not working and "something else" had to be tried.
He said children were looking for an excuse to say no to drugs, against peer pressure, and the scheme would give them that excuse.
"One of the difficulties we have got in our society is that the government has tried so hard and so much to try to improve levels of prevention, yet we are not meeting with enough success," Mr Walker said.
The mixed, non-selective school takes pupils aged from 11 to 19.
Those selected each week will report to the sick room for testing by specially-trained non-teaching staff.
Results will be available three days later.
Mr Walker said that no child would be tested against his or her wishes.
"If a child says no to being tested we will call the parents into the school and discuss it, " he said.
"It might indicate that the child has been taking some stuff and doesn't want to be found out.
"We will then assess what support they need."
The tests will detect cannabis, speed, ecstasy, heroin and cocaine.
A summary of the school's findings will be released every four to six weeks and parents will be informed of their own children's results.
Children who test positive will not be expelled but those found dealing will be and the police will be called in.
Pupils at The Abbey School will be tested from the new term
"It's not a question of punishment, it's a question of support. We will decide whether they need counselling, police support or healthcare," said Mr Walker.
"We do not have a bigger drugs problem than any other school," he said.
"There's a chance we have even less of a problem because we are so pro-active."
Paul Carter, Kent County Council cabinet member for education, said he supported Mr Walker.
"It's very brave of the school. I wish them luck," he said.
"Random drug testing is fraught with legal problems so we are issuing the school with helpful guidance.
"I believe the tests will be a strong deterrent to youngsters dabbling in drugs."