Think it’s hard for schools to get bad teachers out of the classroom? Turns out teachers agree.

More than half of teachers believe it’s too difficult to weed out ineffective teachers who have tenure, and nearly half say they personally know such a teacher, according to a survey released Tuesday evening by the Education Sector, a nonpartisan think tank.

Tenure provides teachers with job security and generally is awarded a few years after educators enter the profession. It is supposed to ensure teachers can’t be fired at the whim of a principal or angry parent.