People who thought teens would be using marijuana more because of Arizona's 2010 medical-pot law are wrong, a new study shows.

Combined, the percentage of 8th, 10th and 12th graders who reported using marijuana at least once in their lives went from 29.9 percent before the law passed to 28.7 percent in 2012, according to statistics in the latest Arizona Youth Survey. Conducted by the Arizona Criminal Justice Commission, the project collected questionnaires from more than 60,000 Arizona students in every county.

Reported marijuana use in the last 30 days also went down, from 14.8 percent in 2010 to 14.3 percent this year.

See also: Teenagers May Get Marijuana From People Who Have Marijuana, Local Media Discovers

Governor Jan Brewer, a staunch opponent to the 2010 Arizona Medical Marijuana Act, remains wary about the impact of the law, says her spokesman, Matt Benson.

"It's too early to tell if we're seeing a true decline in usage," he says.

Still, he admits that the governor "was concerned that the medical marijuana program would lead to an increase an use," and that "we're glad that we havent seen a spike in usage."

A closer look at the numbers reveals that lifetime marijuana use by 10th and 12th graders went up by a few tenths of a percent since 2010, but a 1.6-percent decrease by 8th graders brought the total down for all three grades.

The Arizona Republic and other news outlets focused mainly on the survey's interesting finding that one in nine teen marijuana users, (who themselves are about one-seventh of teens), obtained their marijuana from medical-marijuana cardholders. The survey did not determine if the teens getting the pot from cardholders also got pot from other sources, or if the cardholder had sold the teens pot prior to becoming a cardholder.

But news outlets basically ignored what is arguably a more dramatic finding: That the medical-pot law has not led to an overall increase in teen use, despite pot being in the news constantly in the last two years, and the proliferation of legal home-grown pot and compassion clubs.

We asked Maricopa County Attorney Bill Montgomery today whether he was surprised by the news that fewer teens were using marijuana, or if he expected that result.

Montgomery wrote back, "The decline in reported marijuana use among 8th graders is insignificant when compared to the increase among teens in other grade levels and the substantial proportion of all teens who report they are getting pot from medical marijuana cardholders."

Actually, the decrease among 8th graders was more significant than the increase in the other grades. But we understand his point: Marijuana use by teens is a concern, and so is where they get it.

Will Humble, the director of the Arizona Department of Health Services, which administers the medical-marijuana program, says he won't try to draw conclusions about the survey's findings on just teen pot use. But he is "encouraged" that the survey showed a drop in all substances abused by teens, and a drop in teen drinking and driving.