The Brady Campaign, a leading gun-control group, accused the NRA of "missing the point" by ignoring the need for expanded background checks and other measures the Senate is considering.
"The American public is calling for a comprehensive solution that not only addresses tragic school shootings, but also helps prevent the thousands of senseless gun deaths each year," it said in a statement.
Dan Domenech, executive director of the American Association of School Administrators, said while a trained law enforcement officer with a gun would be valuable, his group opposes arming "a teacher or an employee who simply has taken a course and now has the ability to carry a weapon."
Also denouncing the recommendations was Randi Weingarten, president of the American Federation of Teachers, which represents 1.5 million teachers and other workers. She called it a "cruel hoax that will fail to keep our children and schools safe" while helping only gun manufacturers.
The NRA released its report as congressional momentum seems to have stalled for any sweeping steps to curb firearms violence.
Top Senate Democrats have little hope for a proposed ban on assault weapons, and the prospects for barring large-capacity magazines also seem difficult. Key senators remain short of a bipartisan compromise on requiring gun transactions between private individuals to undergo federal background checks, which currently apply only to sales handled by licensed gun dealers. The Senate plans to begin debating gun legislation next week.
At the White House, spokesman Jay Carney said administration officials were looking for middle ground, and he emphasized background checks, widely seen by gun control advocates as the most effective step available.
"We are working with lawmakers of both parties and trying to achieve a compromise that can make this happen. Especially when it comes to the background checks," Carney told reporters.