Former Drugs Squad officer Dave Parvin took education from the classrooms in Bognor Regis on to the streets.
Mr Parvin gave students at The Regis School the latest information about drugs and their effects in a series of seminars.
All of the some 1,700 pupils attended the sessions. Among them were Pheobe Reeves and Josh Patterson.
Pheobe, 13, said: “I found the seminar really powerful. This type of stuff is aimed at our age groups.
“It was so interesting what type of stuff goes on. We don’t think what the consequences and the risks are.
“We don’t really understand what can happen to us because we are only 13 or 14. We don’t understand what we are doing to ourselves at times.
“We are at the age where we are going to parties and it’s nice to know that other people are also saying no to drugs there. That you are not on your own.”
Josh, 15, said: “It was nice to have a different point of view about drugs to our teachers. We heard about ecstasy, cannabis and cocaine.
“I knew some of it but I found out a lot more – that ecstasy could kill you in ten minutes and that cocaine makes your nose numb and causes scabs and bleeds.”
Mr Parvin spent 12 years as a Drugs Squad officer in Yorkshire and several other counties.
He has been staging seminars in schools for the past 13 years and updates his knowledge to ensure it remains relevant.
He said: “The days of preaching about drugs have gone because that never worked. It’s now about using the hour I have with the students to put over information which is going to have an extremely important effect on their lives.
“I want them to know the risks involved with the drugs that are likely to come in contact with. They need to know that they are dangerous.
“It’s important for the students to know that, despite what they might see on social media, it is normal not to take drugs.”
It was also vital to involve parents as well. Many of them attended an evening session he held at the school.
He said: “We need to have a circle of school, pupils and parents. If everyone works together, then we minimise the risks.”
Katie Robinson, the school’s team leader for personal, health, citizenship and social education, said: “Dave brings a wealth of knowledge to these sessions.
“The students benefit from someone from outside coming in and talking to them about drugs.”
School principal Mike Garlick said: “I can protect children inside school and it’s important I provide them with the information about what life is like outside it.
“My teachers can’t possibly know what the drugs scene is like and that is the big difference in getting Dave involved. He does know that and the children respect his experience with the Drugs Squad. He has been there, seen it and done it.”