Christopher Peregory, 12, had been sent to the principal's office for misbehaving. He had to escape. So he walked out of Fairfax's Belle View Elementary School, hopped a Metro train to Reagan National Airport and -- without a ticket or a boarding pass -- walked onto a Trans World Airlines plane bound for St. Louis.

He took an empty seat in the back and settled in. A flight attendant asked if he'd like a beverage.

No one knew where Christopher was until he called his mother from the St. Louis airport later Wednesday. "He was practically hysterical," said his mother, Renee. She said her son had never run away before. "He's a very good child. It was just an adventure."

She contacted the airport, and child welfare officials took custody of the boy. He returned home Thursday with a plane ticket provided by TWA.

"Boys will be boys," said the Peregorys' lawyer, Ken Bynum, adding that Christopher chose the flight at random. He was less charitable toward TWA. "It's pretty obvious to me they screwed up in more ways than one. This is a 12-year-old. He just walked on."

The Federal Aviation Administration is investigating whether TWA violated airport security procedures. TWA spokesman Jim Brown said the boy blended in with a family boarding the flight, then made himself incon spicuous by sitting near an adult. "It made him look like he was the adult's child," Brown said. "He was apparently a very savvy kid."

Brown said TWA is responsible for checking tickets, but Christopher's behavior must be taken into consideration, too. "It's no different than a juvenile walking out of a retail outlet and stealing several hundred dollars' worth of merchandise," Brown said.

He said TWA has not decided whether to file charges against the boy or seek compensation for the cost of the $676 one-way ticket.

Peregory said her son was about to be sent home from school "for calling a little boy a name." School officials wouldn't comment, saying student records are private.

Yesterday, Christopher was on the ground -- and grounded by his mother.

"TV is out of the question," she said. "He's not supposed to leave the yard. . . . Missouri is definitely out of the yard."