State Department of Criminal Justice data show arrests of Californians under 18 last year were the lowest they've been since 1954.
Arrests fell 20-percent overall, and included a 17 percent drop in felonies.
A law that reduced marijuana possession from a crime to an infraction only accounted for a quarter of the drop.
Mark Males is with the nonprofit advocacy group Center for Juvenile and Criminal Justice.
He says there has been a slight improvement in the economic well-being of the poorest Californians.
MALES: "That is the population that tends to get arrested the most so beyond the socio-economic factors and the change in the marijuana law we're really not able to explain this but we're certainly researching it more."
Males says the drop comes at a time when juvenile incarceration rates at state and local jails are the smallest they've been in more than a decade.