CHICAGO (AP) — Some teachers in the nation’s third-largest public school district who were expected to report to the classroom ahead of students’ return next week stayed home Monday over coronavirus concerns.

Chicago Public Schools announced plans in November to bring students back in phases. Starting next week, preschool and some special education students have the option to return or continue remote learning.

Roughly 8,500 teachers were expected in classrooms Monday. It was immediately unclear how many showed, but those who didn’t said wearing masks makes it harder to teach and they’re concerned about their health.