HOUSTON — As school districts across the country consider placing more police officers in schools, youth advocates and judges are raising alarm about what they have seen in the schools where officers are already stationed: a surge in criminal charges against children for misbehavior that many believe is better handled in the principal’s office.

Since the early 1990s, thousands of districts, often with federal subsidies, have paid local police agencies to provide armed “school resource officers” for high schools, middle schools and sometimes even elementary schools. Hundreds of additional districts, including those in Houston, Los Angeles and Philadelphia, have created police forces of their own, employing thousands of sworn officers.

Last week, in the wake of the Newtown, Conn., shootings, a task force of the National Rifle Association recommended placing police officers or other armed guards in every school. The White House has proposed an increase in police officers based in schools.

The effectiveness of using police officers in schools to deter crime or the remote threat of armed intruders is unclear. The new N.R.A. report cites the example of a Mississippi assistant principal who in 1997 got a gun from his truck and disarmed a student who had killed two classmates, and another in California in which a school resource officer in 2001 wounded and arrested a student who had opened fire with a shotgun.