While Arizona is standing still, however, other states have been making "incredible strides forward," said a spokeswoman for Shared Hope International, which released the report card Thursday.
"Arizona now is becoming one of the lower-ranking states, because other states are advancing while it is not," said Taryn Offenbacher, the spokeswoman.
Where 26 states got an F two years ago, today only six states got the lowest grade. Arizona was one of 17 states with a C this year, the first year the report has awarded an A - which went to Tennessee, Washington and Louisiana.
The Protected Innocence Challenge grades states on 41 key legislative components that it says should be addressed in a state's laws to deal with domestic sex trafficking of minors.
Arizona's worst grade in those categories - an F - came for its laws aimed at protecting child victims of sex trafficking.
But officials said the biggest problem with Arizona law is the so-called "age loophole" that sets harsher penalties for those who have sex with younger prostitutes.
Under state law, a client - or "john" - who solicits sex with someone who is 14 or younger could get up to 27 years behind bars. The penalty drops to a maximum of 21 years in prison if the victim was 15, 16 or 17 years old - but that only applies if prosecutors can prove the john knew the child's age.
Without proof of that knowledge, the minimum sentence can fall to as little as 180 days for soliciting a prostitute who is 15 or older, prosecutors have said.
"There are some gaps in our law that we would like to improve in terms of holding johns a little bit more accountable, particularly with regard to underage victims," said Phoenix Police Lt. James Gallagher, who was in Washington for the release of the report Thursday.
Bills to fix the age loophole have failed in the last three legislative sessions in the state, Offenbacher said.
"It's an ongoing process," Gallagher said of efforts to change the law. He said backers of a change will continue to work toward enhancing the laws "to provide better service to victims in Arizona."
Gallagher said the age loophole hurts police efforts to hold johns more accountable.
"It's our position that we can't quantify somebody's victimization based upon chronological age," Gallagher said. "If you are a minor, you are a minor."
Advocates said cracking down on johns would lower demand, and that "demand drives victimization."
Gallagher said a research project by police and Arizona State University's Office of Sex Trafficking Intervention Research found demand for the sex trade "far greater than we ever expected" in the Phoenix area.
After police posted ads offering sex services, he said, they receive more than 1,000 graphic phone calls and text messages over two-week period seeking sex. Their research estimated that as many as 78,000 men may be looking to solicit sex in the region.
Getting a C again means "there has been a minimum legislative progress this year on the issue of domestic minor sex trafficking" in Arizona, Offenbacher said. Fixing the age loophole would so a lot to improve the grade, and the situation, in Arizona, she said.
"We would say, tighten that law, because that's really the root of the issue," she said.