Heather Wolpert-Gawron has been teaching for eleven years at Jefferson Middle School in San Gabriel, Calif. During that time, she says, the school has had about ten principals.

“We had many years where the morale was low,” she says. “We just kind of felt abandoned.”

Some of those principals left on their own. Some were removed. According to a new report from the nonprofit School Leaders Network, half of new principals quit in their third year on the job.

The group, which provides training and support to principals, says the job has become too complex and isolating. Principals put in long hours overseeing teachers, meeting with parents and implementing one reform after another.

“It’s very demanding and you’re being pulled in different directions, so it really makes it difficult for you to focus on being an instructional leader,” says Connie Rodriguez, who left her position as a junior high school principal in San Antonio, Texas, after three years.

It costs about $75,000 to recruit and train each replacement, says Mariah Cone, vice president of knowledge with the School Leaders Network. The cost to student achievement is higher, she says, with studies showing that both math and English test scores drop when a principal leaves.

“It takes up to three to five years for the next principal to really be able to show gains,” Cone says.

If the next principal lasts that long. Cone says ongoing mentoring and training might help more of them stay longer.