Jordan Pritchard, a former staff sergeant, said he felt "like this is something I had to do" because Gower Elementary School does not have metal detectors or armed guards.
After 26 people, including 20 children, were shot and killed Friday at Sandy Hook Elementary School in Newtown, Conn., Pritchard said he took matters into his own hands to keep his children safe. He does not, though, carry a weapon at the school, WSMV-TV, Nashville, reported Tuesday.
"What this uniform represents, the hope it brings, is larger than any weapon that I would ever need," Pritchard said.
"I said, 'Boy, you don't know how much better I feel having you standing here,'" fellow parent Billy Hester said.
Pritchard said the Marine Corps has asked him to stop wearing the uniform at the school because it is against its rules about which uniforms can be worn in public.
"It was not my intent, when I drug this uniform out of the closest, to upset the Marine Corps. It didn't even cross my mind," he said.
"Strip me of my honorable discharge. Take it away. The peace that these parents and teachers have -- that's enough honor for me."