LEBANON, Ohio — The drug kingpin had six lieutenants and was selling as much as $20,000 worth of high-grade homegrown marijuana every month to high school students, being careful not to do business on school grounds, where they knew it was riskier, investigators said.

And all this before he graduated.

A 17-year-old high school student was at the center of a distribution ring that operated in two Cincinnati-area schools, the Warren County Drug Task Force said Monday.

A yearlong investigation culminated in the arrest of the teen and seven adults, as well as the seizure of more than 600 hydroponically grown marijuana plants with a street value of about $3 million, the agency said.

The student, who was not named, will face charges in juvenile court. He had $6,000 in cash in his bedroom closet, sheriff’s officials said.

‘‘He was selling to six other people who were kind of like his lieutenants,’’ said the commander of the task force, John Burke. ‘‘Then they were distributing the drugs to other high school students.’’

The juvenile told authorities he was not selling marijuana or conducting business on the grounds of the high school, Hamilton County prosecutor David Fornshell said.

‘‘There were strict orders not to sell at [school] because you would get caught and the punishment would be severe,’’ Fornshell said at a news conference.