A Boston high school employee known as “Rev” was charged this week with attempting to murder a student authorities say he had recruited to work for him selling marijuana.

Police and prosecutors say that Shaun Harrison, who had worked for English High School, shot a 17-year-old student in the back of the head Tuesday night. Remarkably, the student not only survived but flagged down a car while he had a bullet wedged in his cheek. He spoke with police in his hospital room the following day.

Harrison, 55, was arrested and charged in Roxbury Municipal Court with attempted murder. He operated “a marijuana distribution enterprise” and had gotten the student to work with him before some sort of still-unspecified dispute, according to the office of Suffolk County District Attorney Daniel F. Conley.

“We’re saddened, we’re shocked by the news,” Denise Snyder, spokeswoman for Boston Public Schools, said in a telephone interview Friday. “I think it was a really sad day for us yesterday.”

Harrison is believed to have regularly mentored the 17-year-old at the school, police said. His nickname, “Rev,” was posted on what was his office door at English High School, which the Boston school system describes as the country’s oldest public high school. (The Boston Latin School, the school’s football rival, says they are the oldest school in the country, predating English by two centuries.)

Kernaham Buck, an attorney for Harrison, told the Boston Globe that Harrison ran a substance abuse program at the school and had a “strong record of accomplishment in the field of human services.” Buck did not immediately respond to a message on Friday.

The mood was tense Friday afternoon at the school, a squat, brick structure located in the Jamaica Plain neighborhood, as the news of Harrison’s arrest dominated city headlines.

Outside the school, a man purporting to be affiliated with Boston English ordered a reporter off school property.

“We’ve had enough with all this Shaun Harrison stuff!” the man yelled. When the reporter stepped onto the sidewalk just off school grounds, the man approached quickly. “I told you to get off school property!” he said.

Prosecutors say that Harrison and the student met up Tuesday night and were walking on Magazine Street in Roxbury, when the older man pulled out a handgun and fired it at the back of the student’s head before fleeing.

The 17-year-old was taken to Boston Medical Center with what police said were injuries that were not life-threatening, after being shot behind the right ear. After the shooting, the teenager flagged down a passing car and asked for help, police said in the complaint filed in municipal court.

In addition to attempted murder, Harrison was also charged with aggravated assault and battery with a dangerous weapon, unlawful possession of a firearm and other counts related to the shooting. While Conley’s office asked that Harrison be held on $750,000 bail, Judge David Poole of the municipal court set the bail at $250,000. Poole also ordered Harrison to wear a GPS monitor, remain at home if released on bail and stay away from the 17-year-old.

Detectives with the Boston Police Department went to Harrison’s home in Boston, just a five-minute walk from where the shooting occurred, and saw three men leaving: Dante Lara, 24; Wilson Peguero, 23; and Oscar Pena, 19. These three were searched and found to have guns, marijuana and a police scanner, and they were also arraigned Thursday.

Conley’s office says any connection between the three men and Harrison’s “alleged drug enterprise remain under investigation,” but prosecutors believe they went to the home to remove evidence. Two of the men and Harrison also have similar tattoos, prosecutors said.

“The investigation into his alleged drug ring remains very active,” Conley’s office said in a statement.

Snyder said that school officials learned of the allegations on Wednesday afternoon, found out he was arrested that night and fired him the following morning. He had started working as a coordinator at English High School, where his title was “dean of academy,” on Jan. 5, after having worked for three other Boston schools since 2010, Snyder said.

His role at English involving helping provide what are known as “wraparound services” for students, Snyder said. These generally involve offering social services to students, finding disciplinary options other than suspensions or helping homeless students find housing. A report issued last year by the Massachusetts Budget and Policy Center noted that the strongest types of these services involve a specific point-person to make sure “the social-emotional support responsibilities do not fall unduly on teachers and principals.”

The situation involving Harrison is “an isolated incident,” Snyder said,  adding that counselors and psychologists were being made available to anyone at the school who needs support.

“Nothing is more important than the safety and well-being of our students,” John McDonough, interim superintendent of Boston Public Schools, said in a statement. “English High School is filled with committed and caring educators who go above and beyond for their students every day. This school community is strong and its students and teachers have my unwavering support.”

Snyder said school officials have received a few dozen phone calls about the situation, most of which involved people wanting to make sure Harrison was not returning to the school.

John Wolfson in Jamaica Plain, Mass., contributed to this report.

[This post has been updated.]