My mother had a bachelor’s degree in education but chose to work only as a substitute teacher. The exception was when my brother and I were in college, and her full-time salary paid our tuition, room and board.

I have long been interested in how substitute teaching works. Two decades ago I wrote a column about Mom’s experiences. Lately I have been conversing with K.M. Dawson, a sub in the Midwest who has much to say about her 12 years in that line of work, including why substitutes should be used less than they are.

Despite the assumption that school kids torture subs, Dawson said she rarely has trouble controlling a classroom. “Usually, if there is one troublemaker, the other students tell him to settle down,” she said.

But she experienced one sixth-grade classroom that was totally out of control. She blamed that on the fact that the teacher she was substituting for had been hobbled by a leg cast. Her students were used to her being unable to stifle misbehavior quickly, Dawson figured. She discarded that explanation when she substituted for a different teacher at the same school the following week and found that class also unmanageable.

When she mentioned the problems she had had to another sub at a different building, the woman correctly guessed the name of the troubled school. She told Dawson that she absolutely refused to sub there. Other subs she knew also ignored its calls.

Dawson heard later that the problem was the principal, who didn’t support teachers, didn’t visit classrooms and didn’t get involved in disciplinary problems. If a teacher sent a misbehaving student to the office, the secretary just had the child sit there for a while.

Dawson knew of a principal with a different approach. He became an administrator because he needed the extra money. But he loved teaching so much that he often covered absences himself. Teachers who visited a classroom where he was subbing would find him sitting on the desk and asking questions like, “What would you have done about slavery if you were Lincoln?”

The districts Dawson subs for have computerized systems that send out mass robocalls or email notifications. The first teacher to accept gets the gig. “I normally never meet the teachers I am subbing for, and I’m not sure if they know my name,” she said. People who want a general substitute’s license must fill out an application, submit their college transcript, pay to be fingerprinted for a background check and send in a fee. When they receive their license they can take a copy and register at any school where they want to work.

“Over the years I have subbed at five schools, signing up the summer before,” she said. “One decided I was not a good fit. I don’t know if it was my teaching or the fact that it was a half-hour away and by the time I got called and got there I was barely ahead of the students. Another school dropped me because they had laid off a lot of teachers and decided they would concentrate on using them as subs.”

When she accepts an assignment, she signs in at the school office, where she gets a room key and a lesson plan. “The regular teachers who are present when I sub are very helpful and welcoming and not at all condescending to those of us who don’t have a teaching background,” she said.

Occasionally, students tell her she is violating the classroom’s routine by insisting on engaging students in conversation about the lesson. “One class told me their teacher mostly just gave them paperwork and then read while they did it,” Dawson said.

On a day when she was assigned to go from class to class helping students who had learning disabilities, she encountered a sub “who handed out the worksheet, put his feet up on the desk, pulled a hat over his eyes, and went to sleep.” She decided he was having a bad day. When she saw him doing the same thing a week later she notified the school office.

Dawson’s opinion, after handling so many different classes, is that our traditional reliance on subs can be harmful. There is no adequate substitute, she said, for a full-time teacher who knows how much every child has learned and exactly what they need to move forward. She said schools would improve learning if they required teachers to be in class unless they are sick or have an emergency.

“The day I subbed for a physics instructor he was out of the classroom because he was the golf coach and had to leave with the team on Friday morning to get to a tournament,” she said.

At one school, she subbed 24 days over a few months and kept a record of each assignment. Only three times was the teacher absent because of illness or an emergency. Instead, Dawson said, she was called in to cover classes because teachers were “in the state capital involved in salary negotiations, in the school library learning new technology, meeting with others in the department to discuss the standards for the next year, or grading the practice standardized tests.” She said the teachers are not to blame for such chores or their scheduling, since higher-ups do that.

Dawson also thinks that students should stay in class when school is open. She has had lessons interrupted by students leaving to applaud a graduating senior parade, or attend a competition, or be in a team photo, or watch a student talent show. One student described to her a required assembly with these words: “famous athlete did drugs and ruined career and doesn’t do drugs now and we shouldn’t.”

Subbing is retirement income for Dawson. She started filling in for teachers when, at 59, she lost her job as a circulation manager for a local newspaper that depended on teenagers to make deliveries. A neighbor who was a retired teacher suggested to Dawson that her experience with that age group would be valuable in the classroom.

Dawson likes working with kids, just like my mother, who subbed into her 70s. Dawson finds much to amuse her, like discovering that students these days don’t know the meaning of terms such as “blackboard” or “telephone book.”

The calls to sub this year haven’t come in for Dawson yet. She is thinking about it.