By Andrea Lucia, CBS 11 News

DENTON (CBSDFW.COM) – A Denton County attorney is challenging the way statutory rape cases are tried in Texas courts, and his argument could have an impact nationwide.

In April, Richard Gladden argued before the Texas Court of Criminal Appeals that his client’s conviction for the rape of a 13-year-old girl was unconstitutional.

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Gladden alleges the sex was consensual and that his client, Mark Fleming, believed the girl was an adult.  “It’s not fair to hold someone criminally responsible for conduct when they have no mental state – or no intention of doing anything wrong – or knowledge that they’re doing anything wrong.”

His efforts have attracted the support of women with sons on the sex offender registry.  Among them is a North Texas mother, who asked to remain anonymous.

“I don’t want any other mother to feel the way I feel,” she told CBS11.

Her son was stationed at a Marine Corps air base in Yuma, Arizona, in 2009, when he met a girl.  “Just tickled pink, falling head over heels for her,” she recalls.

Pages from her Facebook and MySpace accounts claim she’s 18 or 19 years old and a student for the University of Texas at Austin.  The military mom said she never suspected the girl her son was dating was actually only 13.

“It never dawned on me.  It never crossed my mind, and then when it all fell through and came to light, it felt like someone had punched me in the stomach,” she said.

Her son, she says, was convicted of rape, dishonorably discharged, and sent to prison.  He wasn’t alone, though. His mother says, she soon learned 11 Marines in all were arrested for separate sexual encounters with the same girl, including a second young man from North Texas.

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CBS 11 spoke to his mother, as well. She also asked to remain anonymous, but said her son’s plans for a career in the military were cut short by his arrest.  “He told me, ‘I did not know she was that young’”, she said.

It’s unclear if these women’s sons would benefit from Gladden’s success.

Hundreds, if not thousands of men, though, would likely be able to contest their convictions – or get their names off the sex offender registry, if the Texas court rules in his favor. It would also permit future defendants to argue they were misled or had reason to believe their victims were of legal age.

If the Texas justices rules against him, though, he plans to appeal to the U.S. Supreme Court, where he is confident he would ultimately win.

“It would change the law in about a third of the country,” said Gladden.

At the Dallas Area Rape Crisis Center, that possibility is causing concern.

“I think it’d be a huge step backward for victims,” said Director Jana Barker.

While she admits children don’t always look their age, she doesn’t believe a 13 year old could fool anyone.

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“An adult male can’t tell this is an eighth grader?  C’mon,” she said.