A Washington court's ruling this week that teachers can legally have sex with their 18-year-old students is sparking outrage among parents, psychologists and sex therapists.

A three-judge panel of the Washington Court of Appeals on Tuesday ordered the dismissal of a case brought against Matthew Hirschfelder, a former choir teacher at Hoquiam High School who was accused of having a sexual relationship with an 18-year-old student in 2006, when he was 33.

Hirschfelder, who resigned in 2007, denied the relationship. But his lawyer challenged the charge against him, first-degree sexual misconduct with a minor, arguing that an 18-year-old is not a minor. The Court of Appeals heard the case after a lower-court judge refused to dismiss it.

With Tuesday's ruling, the appeals court unanimously agreed that the state law banning sex between teachers and students is "ambiguous," because 18-year-old students are not legally minors. The appeals court reversed the lower court's ruling and ordered it to dismiss the charges.

Prosecutors say they have not decided whether they will appeal the ruling to the state Supreme Court.

"I'm shocked and surprised," Connie Severson told FOXNews.com. "They're going to be teaching our students and the last thing you want is sexual relations on their mind."

Severson, whose son Stephan is a junior at Hoquiam High School, said the ruling has "opened up the eyes of other parents" in the district.

"This shouldn't be OK," she said. "They are teachers. Every one of them should know better."

Severson said the ruling could dissuade parents from enrolling their children within the Hoquiam school district.

"I'm hoping from a parent's perspective that when my daughter is 18 and dating that she's not having a relationship with her teacher," she said. "This is not college, it's not a university, this is high school."

Dr. Judy Kuriansky, a clinical psychologist and sex therapist, said the ruling sends a "very bad message" to students and teachers alike.

"Normally I would respect what the courts have to say, but this is a highly inappropriate message and one that is potentially dangerous," Kuriansky told FOXNews.com. "This is where ethics come in conflict with the law."

Kuriansky said the trauma that can be associated with such a relationship can last long after early adulthood.

"It can be very traumatic and be buried and repressed in their minds, and then emerge 10, 20 or even 30 years later when there is some kind of trigger or similar experience," she said. "It has the potential to create tremendous tension and trauma."

Dr. Yvonne K. Fulbright, an author and sex educator, said other potentially troubling scenarios could arise and become somewhat acceptable due to the ruling in Washington. One such scenario, she said, would be a female student who is vying for the attention of an older male teacher.

Having a relationship with an older man could be seen as a status symbol, she said, but "It can certainly rob a person of their natural growing-up process and having first experiences with someone their age."

Overall, Fulbright, who writes the SEXPert column on FOXNews.com., said young women who have sexual encounters with older men typically become sexually active sooner, which can lead to reproductive issues.

Despite the court's ruling, Hoquiam High School Principal Mark VandenHazel said it's still not acceptable for teachers to engage in sexual conduct with 18-year-old students.

"Regardless of whether it's a criminal act or not, you do this as a teacher and you're just not going to have a job," VandenHazel told FOXNews.com. "We have zero tolerance. If you want to continue teaching, don't even think about it."

Rich Wood, spokesman for the Washington Education Association, echoed VandenHazel's comments.

"A teacher who has an inappropriate relationship with a student is subject to losing their certificate and getting kicked out of the association," Wood told FOXNews.com. "It is grounds for never teaching again in this state — that's not affected by [the Hirschfelder ruling]."

State legislators have already introduced a bill that would make it a felony for teachers to have a sexual relationship with a student who is between 16 and 21 years old. A conviction would carry a mandatory minimum of five years in prison.

"The expectations of parents when they send their kids to school is that they get an education and not be groomed for some quid pro quo relationship that might occur," said Rep. Larry Haler, who introduced the bill Tuesday. "The message [the ruling] sends is one that basically says that there's really nothing wrong with this kind of behavior by school staff, or even on the part of students.