This year, more than 60 teachers have resigned since July. The district currently has about 70 teaching vacancies. At the end of August last year, there were about 177 teaching vacancies for a staff of fewer than 2,000 teachers.

This constant turnover strains school quality. In the 2015-2016 school year, just 83 percent of classes in the district were taught by highly qualified teachers, meaning they were certified to teach their assigned subjects and grade level. In a couple of St. Louis schools, only half of the teachers were highly qualified.

Statewide, 96 percent of Missouri’s teachers were highly qualified.

“We’re fighting an uphill battle,” Superintendent Kelvin Adams said.

School officials tend to say that teachers leave for better-paying jobs. St. Louis officials also acknowledge it’s more challenging to teach in urban schools, where there are more students coming to school with trauma and toxic stress. But they point out that teachers do have a chance each spring to resign.

However, several of the 32 teachers being sued say they left St. Louis Public Schools not because it was difficult to teach students, but more because they felt they had no support from administrators.