On Monday, red ribbons will be passed out to the students to pin onto their clothes or book bags showing that they are committed to saying "no" to drugs.
"Drugs can really hurt you. They can mess up your life," said Matt Clopper, 9.
Clopper and friend Brandon Brechbiel, 10, who play a variety of sports, said they plan to keep away from drugs throughout their lives.
Speaker Steve McTaggert, social issues teacher at Greencastle-Antrim Senior High School, told the group he often was pressured as a football player at his New Jersey high school and as a college student at Shippensburg University "to get larger" by taking drugs.
But he never gave in to the pressure, he said.
"I'm glad today I didn't," he said. "As you get older, there will be more and more temptations. Take it from me, it gets you nowhere."
Drugs cloud your mind and you can't think straight, a bad combination when you're behind the wheel of a tractor-trailer hauling an 80,000-pound load, said Mike Shilling, freight operations manager for Con-Way Central Express trucking company of Hagerstown, co-sponsor of the anti-drug campaign.
"Think about it before you do it," said Gary Roberts, who manages 65 drivers at the trucking company.
A truck driver for 20 years, Roberts told the students he's seen too many accidents on the roadways as a result of drugs.
"The reason for this program is to get you kids to realize, while you're growing up, why drugs are bad," he said.
Ben Thomas, an officer with DARE, an acronym for Drug Abuse Resistance Education, encouraged the fourth-graders to set goals, but warned them that taking drugs would destroy them.
"If you want to be a winner, continue to set goals and you can be a winner," Thomas said.
The program is also sponsored by GA Cares, a community group that provided T-shirts to the students, and by the Greencastle-Antrim Elementary Parent Teachers Association.