According to a new report from the Colorado Department of Public Health and Environment (CDPHE), cannabis consumption by teenagers in that state "has not changed since legalization either in terms of the number of people using or the frequency of use among users." That conclusion is based partly on data from the National Survey on Drug Use and Health (NSDUH), the same source that prohibitionists cite when they claim legalization has boosted adolescent pot smoking in Colorado.
The difference is that the CDPHE pays attention to confidence intervals, which show that nominal increases in marijuana use have not been statistically significant. Here is the CDPHE's graph of NSDUH prevalence numbers for teenagers, which also includes data from the Health Kids Colorado Survey (HKCS):
NSDUH's sample of Colorado teenagers is much smaller than the one used in HKCS, which is why the prevalence estimates are three-year averages. But taking into account the margin of sampling error, neither survey shows an increase in adolescent marijuana use since legalization took effect at the end of 2012. The picture remains the same if you include the most recent NSDUH numbers, which show a statistically insignificant drop in past-month use between 2013-14 and 2014-15, the period when state-licensed marijuana stores began serving recreational consumers in Colorado.
Another hopeful development noted in the report: Marijuana-related calls to the Rocky Mountain Poison and Drug Center, which rose after legalization for three years in a row, fell from 229 in 2015 to 201 in 2016. The center received 40 reports of marijuana exposures involving children 8 or younger last year, down from 48 in 2015.