BOSTON (AP) — Colleges remain inconsistent in the way they handle athletes’ concussions, according to a Harvard University study that comes more than four years after the NCAA began requiring schools to educate their players about the risks of head trauma and develop plans to keep injured athletes off the field.

In a survey that included responses from 907 of the NCAA’s 1,066 members, researchers found that nearly one in five schools either don’t have the required concussion management plan or have done such a poor job in educating their coaches, medical staff and compliance officers that they are not sure one exists.

The study was co-written by Harvard researcher Christine Baugh and published this week in the American Journal of Sports Medicine.