Joel, a 17-year-old high school student, took the witness stand in a federal courtroom Monday spoke about the trauma he experienced in a school locker room last October.

"Someone next to me tapped me on the shoulder and said, 'Turn around.' I turned around and a girl was standing there," he said.

"I scrambled to get everything into my locker so I could get out of there," the teen added. "I felt really humiliated. I was standing in my underwear."

This wasn't some prank. This was the result of a policy of the Boyertown Area School District that was the focus of a day-long hearing before U.S. Eastern District Judge Edward G. Smith in Easton.

Joel, another boy, and two female students are challenging that new policy, which allows transgender students to choose which school bathroom to use, based on their "gender identity" rather than their physical sex.

The four students who are contesting the policy, which was in force for months before being ratified by the school board in May, are asking Smith for a preliminary injunction to forbid the district from enforcing it while their lawsuit is fought out. They are represented by the Harrisburg-based Independence Law Center and the Alliance Defending Freedom.

On the other side, helping to defend the school's restroom policy, is the ACLU and the Pennsylvania Youth Conference, which promotes the interests of LGBT teens.

Joel, who testified under a pseudonym, was the second student who took the witness stand Monday. He was preceded by "Mary," a girl who said she was unpleasantly surprised in March to see a boy - who district officials said identified as female - in a girls' restroom.

Joel's and Mary's testimony closely meshed. Both painted the district's bathroom policy as an invasion of their privacy. "I have every right to use the male bathrooms and expect privacy," Joel said.

Dr. Scott Leibowitz, a psychiatrist affiliated with The Ohio State University and the Nationwide Children's Hospital in Columbus, Ohio, was the first expert witness called by the district's backers.

Questioned by attorney Ria Tabacca Mar of the ACLU, Leibowitz insisted that preventing transgender students from using the bathroom that fits their gender identity could harm them psychologically.

"It erodes your psychological well-being," he said. "It sends a message that...who they are is not valid. It's society reducing them to their genitals."

About 1.4 million U.S. adults identify as transgender, he said, adding that there are no statistics for adolescents. "This is not chump change," Leibowitz said. "You're talking about a significant number of people in this world who are experiencing this."

"Society has not caught up," he said.

Attorney Gary McCaleb of the Alliance Defending Freedom, criticized Leibowitz's opinions as being "outside the mainstream of medicine."