During your school days, the only monitor you ever encountered was likely in the hall or guarding some kind of pass in your classroom, such as for the restroom. But for several decades in the early 19th century, student monitors reigned supreme over their peers in American schools—because they were the de facto teachers.

At the time, there were not enough educators to go around in America’s burgeoning school system, so the few teachers outsourced many of their duties to the students themselves. They did so with the help of “monitors,” a select group of students teachers allowed to instruct other students—and not just pupils their own age.

The monitorial system, as it was called, was popular in much of the northeastern United States in the first 30 years of the 19th century. Here’s how it worked: When school began, the teacher taught a lesson to the monitors, a cadre of students selected for their high exam scores or exemplary character. Then, these monitors would go back to their classes and impart the lessons to other students.

The system had practical benefits: It allowed one teacher to instruct huge groups of children, and in many cases did not even require the use of books. It was orderly and regimented. In the words of education administrator Ellwood P. Cubberley, “the teacher had only to organize, oversee, reward, punish, and inspire.” And given the shortage of schoolteachers in the early 1800s, it was even more attractive for towns and cities that needed to educate their children.

Students didn’t always govern themselves in early American classrooms. In the small one-room schoolhouses of the 18th century, students worked with teachers individually or in small groups, skipped school for long periods of time to tend crops and take care of other family duties, and often learned little. Others didn’t go to school at all, taking private lessons with tutors instead.

That laxity was unacceptable for a British teacher named Joseph Lancaster, who invented a system to counter it. By the early 19th century, his system had migrated to the United States—and convinced many cities that they could afford a school. Even before public school was required in Pennsylvania, cities like Harrisburg set up their own free schools using the system. Maryland briefly had monitorial schools statewide in the 1820s, and other states participated, too. Between 1806 and the 1830s, Lancaster and his monitors dominated classrooms in the U.S. The system was even used by missionaries to instruct Native American children through the 1840s.

A school run on the Lancaster principle looked different than any you’ve ever attended. Instead of being separated into different classrooms by grade or subject, students of all ages sat in rows in a single room. They were separated into classes not by age, but by their mastery of certain subjects.

Monitors were responsible for almost every aspect of classroom management—catching up kids who had missed class, examining students and promoting them to different classes, taking care of classroom materials, even monitoring the other monitors. Schools ranged in size from a few students to thousands. Monitors had heavy workloads, but aside from a few special privileges and some serious rank within their classrooms, they were unpaid.

In larger schools, the monitor’s lessons might take place at a designated “station” in the classroom, where monitors used pre-printed cards provided by their teachers and attached to the wall as visual aids for their fellow students. In smaller schools, students might simply gather around the monitor and learn the lesson by ear.

Once they had memorized their rote lesson or completed the assigned written work on a slate, class members would demonstrate it for the monitor. A new lesson would be assigned to the monitors and the school day would continue.

Lancaster compared the system to an army that produced “admirable order.” A schoolmaster, he thought, was only as good as his monitor. Monitors rose to their rank after acing special exams and were given special privileges. Some wore special badges and the position was a mark of pride.

There were other reasons to be proud in a monitorial classroom. When people moved up a class, they were rewarded with praise or small prizes they could “purchase” with tickets received for good conduct or correct lessons. However, moving down a class—being demoted because of poor scholarship—was regarded as a humiliation.

At the time, teachers were not well respected or well paid. Schoolmasters (nearly all teachers and pupils in the system were men) were hard to come by and usually poorly educated themselves. Those who did have an education or teaching experience often ditched their careers early on for more lucrative professions until women took over the profession in the 1840s. Women were much less likely to leave their teaching jobs, as there were few other professional options for them.

That made Lancasterian schools (and Bell or Lancaster-Bell schools, named after a nearly identical system invented by Andrew Bell around the same time) particularly attractive to school boards. The system put the brunt of the work on monitors, not teachers.

But that didn’t sit well with some parents. They complained that their children were spending more time teaching than learning and that the schools’ focus on rote memorization never taught them other skills.

Over time—and especially after the 19th-century reformer Horace Mann introduced the idea of professionalized education, common curricula and age-based class grouping—the idea died out. Monitors were relegated to halls and passes.

But the idea of students teaching other students didn’t entirely fade. Peer tutors are still used in the United States, while “pupil-teachers” assisted teachers for half a century after Lancastrian schools disappeared in England. Eventually, they were diverted into their own schools, which became England’s system of teacher’s colleges.

These days, Lancaster’s system seems misguided and impersonal, and the student-teacher ratio would make any school board blush. At the time, though, it seemed like an opportunity. Any education was better than none—even if a monitor, not a teacher, passed it along.