WASHINGTON — The Supreme Court tightened limits on student speech yesterday, ruling against a high school student and his 14-foot-long “Bong Hits 4 Jesus” banner.

Schools may prohibit student expression that can be interpreted as advocating drug use, Chief Justice Roberts wrote for the court in a 5–4 ruling.

Joseph Frederick unfurled his homemade sign on a winter morning in 2002, as the Olympic torch made its way through Juneau, Alaska, en route to the Winter Olympics in Salt Lake City.

Mr. Frederick said the banner was a nonsensical message that he first saw on a snowboard. He intended the banner to proclaim his right to say anything at all.

His principal, Deborah Morse, said the phrase was a pro-drug message that had no place at a school-sanctioned event. Mr. Frederick denied that he was advocating for drug use.

“The message on Frederick’s banner is cryptic,” Justice Roberts said. “But Principal Morse thought the banner would be interpreted by those viewing it as promoting illegal drug use, and that interpretation is plainly a reasonable one.”

Mr. Morse suspended the student, prompting a federal civilrights lawsuit.

Students in public schools don’t have the same rights as adults, but neither do they leave their constitutional protections at the schoolhouse gate, as the court said in a landmark speech-rights ruling from Vietnam era.

The court has limited what students can do in subsequent cases, saying they may not be disruptive or lewd or interfere with a school’s basic educational mission.