WEST PALM BEACH (CBS4) – An undercover investigation at South Florida high schools has led to the arrest of nearly 30 high school students for selling drugs on campus.

The nine-month undercover operation dubbed “Operation D Minus” was designed to crack down on drug sales in schools. Officials said Monday that Palm Beach County School District police posed as students at three high schools. They went to classes, did homework,  and bought drugs from fellow students.

READ MORE: Jimmy Butler Scores 41, Heat Take Game 1 From Celtics 118-107

Most of the arrests were made last week, including 11 students from Royal Palm Beach High, 10 from Jupiter High, 3 from Park Vista High, 3 from William T. Dwyer High, one from Independence Middle school and two home-schooled students. In addition, a 20-year-old adult education student and an 18-year-old dropout were charged.

They were all arrested on charges of selling marijuana or other drugs within 1,000 feet of a school or park, car burglary, and trespassing on a school campus. 

READ MORE: MDFR Identifies "Voice In The Rubble" Victim

Only the high school principals knew which “students” were officers.

Officials say the officers will continue posing as students, though they might move to other schools. Operation D Minus is expected to continue through next year.

The school district recommends expulsion for students selling drugs near schools.

MORE NEWS: Opera Singer, Fashion Designer Radmila Lolly Thrills Miami Heat Fans With Custom-Designed Ball Gowns

(©2011 CBS Local Media, a division of CBS Radio Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)