Williamson County Schools spokeswoman Carol Birdsong said schools can’t risk interference for teachers when 35 percent of their evaluations are based on student learning gains on standardized tests.

Tennessee’s new teacher evaluation system has prompted some school districts to ban student teachers from working in core high school subjects, college education officials say. The reason: So much of a teacher’s evaluation is now based on student test scores that some teachers don’t want to cede control of their classroom to a student teacher.

“It’s nothing but the teacher evaluation system that’s got them tied up in knots,” James Stamper, director of student teaching for Belmont University, told The Tennessean. “We all had to have somewhere to start.”

Recent changes in state law—including teacher evaluations and toughening the curriculum—allowed Tennessee to win $500 million in the national Race to the Top education grant competition.

At the end of this school year, principals will compile assessments on every Tennessee teacher: 35 percent from learning gains, 15 percent from other student-selected data, and 50 percent from classroom observations. Teachers can lose tenure if they score in the two lowest ratings for two consecutive years, and they can gain tenure only if they score in the top two ratings for two consecutive years.

Williamson County Schools spokeswoman Carol Birdsong said schools can’t risk interference for teachers when 35 percent of their evaluations are based on student learning gains on standardized tests.

“It’s your classroom, and you are being evaluated based on your students’ performance,” she said.

Middle Tennessee State University student Starla Weatherell, who will get her master’s in business education in May, is uncertain about where she’ll student teach.

“It’s a huge problem for me, when I live in Williamson County, to not be able to student teach where I want to work,” she said. “Right now, they are telling us we may have to drive two hours.”