I taught at the Mission Hill School. It was a disaster, but it didn’t have to be.

Mission Hill didn’t fail because its mission was impossible to achieve; it failed because it fostered a culture of laziness, incompetence, and defiant isolationism.

The Mission Hill K-8 School was a great idea; its execution was a nightmare. As a former teacher there, I was appalled — but not the least bit surprised — by the results of the investigation into the school’s culture and long list of criminal conduct, which was ordered by Superintendent Brenda Cassellius and published last week. I fully support the School Committee’s decision to close the school, and wish it had been done years earlier.

I didn’t always think this way. In fact, the Mission Hill School was once my dream place to work. After not receiving a job offer the first year that I interviewed there, I returned the next, determined to teach at this internationally-renowned progressive school. I had read the books written about the school, watched the 10-part documentary screened at conferences around the world. After teaching second grade at other Boston-area schools — which were obsessed with test scores, treated children of color like criminals, and crammed school days with as much academic content as they could — I was relieved to be offered a position at a school that valued every child’s individuality and autonomy, placed racial justice at the core of its philosophy, and embraced a varied, creative approach to teaching and learning. At least in theory.

The red flags were there — they were practically jumping out at me, waving and screaming. At a job fair for progressive educators, I met a woman who was leaving Mission Hill. The school isn’t what it claims to be, she told me. It’s sad, because it could be so much better.

When I arrived at the school for my interview, there were dozens of children roaming the hallway. Some of the middle schoolers were engaged in what seemed to be a physical fight; one teacher poked her head out of a classroom, looked at them with a look I later came to recognize as resignation, then looked away. The third and fourth grade classroom was much calmer — the students were scattered around the classroom, independently engaged in a variety of activities: drawing, snacking, building with Legos, flipping through picture books. I was impressed. This is what third grade should look like, I thought: Children leading their own learning at their own pace. At the time, I didn’t know that not a single one of them knew how to read.

For progressive schools to work, teachers must be highly-trained — much more so than in traditional schools because they must guide a complex and ever-shifting course of academic and socioemotional development, anticipating future needs and preparing materials in accordance — for every single student. Within a democratic governing structure, they must be guided by a capable leader who continually earns the trust of students and families — and, crucially, is able and willing to occasionally make hard, even unpopular decisions in service of students.

When I started working there, as an ESL teacher to students in grades 1 through 7, I quickly came to understand what Mission Hill failed egregiously to live up to the ideals of progressive education — and why. Some of these reasons are covered in the report, such as teachers attempting to compensate for systemic injustices in ways that actually perpetuated these injustices. (Numerous educators, including the principal, for instance, turned a blind eye to sustained aggravated sexual assault by a Black boy in kindergarten because they didn’t want to report him to a disciplinary system that over-disciplines Black boys.) Faculty refused to follow individualized education plans because they didn’t want to force students to conform to standardized expectations of what learning should look like or how it should occur. When a highly-qualified special education teacher objected to this practice — noting that, among other things, it was against the law — he was bullied by other teachers and his contract was not renewed.

But many of the reasons for Mission Hill’s criminal negligence have not been discussed. The school had some truly excellent teachers, all of whom taught the school’s preschool and kindergarten children, but also some of the worst teachers I have ever encountered. One teacher, who often spoke about the need to recruit Black men like himself to the teaching profession, never prepared for class, routinely yelled at students, and sent kids who “acted up” out of class to wander the halls every single morning. More than one of his students was labeled too difficult to teach and forced out of the school. Another teacher, who taught third and fourth grade, routinely complained about children in front of her and seemed unable to write at a fourth-grade level herself. I wasn’t surprised to read in the report that she slapped a child so hard that it left marks.

When the school was faced with its own failings, the principal and faculty placed blame everywhere but themselves, refusing to ever entertain the possibility that their culture or teaching needed to improve.

All of this will leave lifelong emotional and academic scars on students. All of it was avoidable. And, most importantly: none of it is intrinsic to progressive education. Running an urban public progressive school is very hard; to succeed, every single teacher needs to be expert — and held accountable within a system that provides sufficient resources, training, and guidance. Effective urban progressive schools are rare, but they do exist.

Mission Hill didn’t fail because its mission was impossible to achieve; it failed because it fostered a culture of laziness, incompetence, excuses, and defiant isolationism. I hope Boston Public Schools has learned its lesson — but let’s make sure it’s the right one.

Emily Kaplan lives in New York.