When Andrew Martinez arrived at Greater Egleston High School Monday, he wasn’t prepared for the news he received .

“You’re not enrolled here,” an administrator reportedly told him.

Although Martinez was planning to finish high school there this year, the 19-year-old is one of 104 students who were un-enrolled from the alternative high school this fall apparently without notification or explanation.

“I’ve been here three years already,” he said, standing in front of the School Street entrance to the building. “How can I be dropped?”

Nearby, also contemplating her educational future was Yokasta Baez, a 21-year-old Roxbury resident.

“I got a letter informing me I was enrolled,” she said. “I didn’t find out until the first day of school when I went to get my bus pass that I wasn’t in the system.”

Martinez, Baez and other students interviewed by the Banner said Greater Egleston staff members were equally in the dark about the sudden drop in enrollment at the school, which specializes in helping students who have fallen behind.

“They’re very supportive,” Martinez said of the staff.

“They help you a lot,” Baez added. “If you don’t come to school, they call you. They want to see you graduate.”

Greater Egleston High School’s student count has dropped from 185 to 79, according to a posting from an anonymous source on the Universal Hub news website. The abrupt mass un-enrollment at the school comes just days before the district calculates official enrollment numbers — a process through which Boston Public Schools determines the per-pupil funding each school will receive.

So how did this happen? A BPS spokesman declined to answer questions about the un-enrollment or the implications for the school’s funding, and instead emailed a statement to the Banner.

“Boston Public Schools is working to ensure all of our young people have access to as many viable education options as possible, including Greater Egleston High School and other alternative education schools and programs,” the statement reads. “BPS is in the process of informing students who are trying to enroll in Greater Egleston High School directly at the school to instead visit the BPS Re-Engagement Center to begin attending classes at Greater Egleston as soon as possible.”

The sudden decline in enrollment at alternative schools has sparked fears among parents that the school department is seeking to close the schools — a politically unpopular move. The BPS spokesman contacted by the Banner would not comment on what effect the loss of 104 students might have on Greater Egleston’s funding or future, referring a reporter back to the emailed statement.

“Unfortunately we cannot comment beyond the statement today,” the spokesperson said.

The chaos at Greater Egleston comes as Dorchester Academy, another high school catering to students at risk of dropping out, faces its own uncertainty. As the Boston Globe reported last month, BPS officials laid off three administrators at the Fields Corner school and sent students letters urging them to visit the BPS Re-Engagement Center. While Dorchester Academy was declared “underperforming” by the state, Greater Egleston is rated as Level III — in the bottom 20 percent of schools statewide, but not in danger of imminent state takeover. But because Greater Egleston often enrolls fewer than 10 sophomores, few students there actually take the MCAS exam, the prime metric the state uses to determine a school’s status.

Greater Egleston has a reputation of working with students who face significant challenges completing high school. Many students work. Some, like Baez, have children. Many students take online courses.

For Baez, who has already paid for child care so she can attend school, the clock is ticking. She has just months before her 22nd birthday to obtain her high school diploma through BPS. Once she turns 22, she can no longer enroll in a BPS school.

“I don’t want a GED,” she said. “I want a diploma.”