WASHINGTON >> An advocacy group for police officers assigned to secure the nation’s schools has a simple message about arming teachers: Don’t do it.

The National Association of School Resource Officers said Thursday it strongly recommends that no firearms be allowed on a school campus except those carried by carefully selected, specially trained police officers. The organization, which has about 4,500 members, provides specialized training for law enforcement officers assigned to work in the nation’s schools.

President Donald Trump said Thursday that highly trained teachers who are armed would act as a deterrent to attackers. He said attackers are not going to walk into a school if 20 percent of the teachers have guns. He then went on to say the right number “may be 10 percent, it may be 40 percent.”

The officials association released a statement that arming teaches increases the prospect that officers responding to an incident may mistake a teacher or any other armed person not in uniform for an assailant.

The group also said that officers receive extensive training. That training includes securing their weapon so that others can’t get to it and shooting in simulated, high-stress conditions. Anyone without such frequent, ongoing practice will likely have difficulty using a firearm safely and effectively. School resource officers also practice how to quickly evaluate the risks of firing. They hold their fire when the risks to others are too high.

The group warns that anyone who hasn’t received the extensive training provided to police will likely be mentally unprepared to take a life, especially the life of a student assailant.

Instead of arming staff, the group is recommending that federal, state and local governments provide enough money to place at least one school resource officer in every school in the nation, and more than one for the largest schools.