States that set out a decade ago to trim prison costs have learned that success lies in a few areas — rolling back draconian sentencing that drove up prison populations in the first place, and remaking parole and probation systems, which have, in numerous cases, sent as many or even more people to jail for rule violations as the courts do for new crimes.

Significant progress has been made on both fronts. Yet New York, a national leader in reducing its prison population, could do much more to reform its parole and probation systems.

These systems were established across in the United States in the 19th century. The premise was that steering people who commit minor offenses to probation, rather than prison, and shortening prison sentences with parole in exchange for good conduct further the goal of rehabilitation. But that notion fell out of favor after the country embraced mass incarceration in the late 20th century, driving up the prison population from about 200,000 at the start of the 1970s to a peak of 1.6 million at the end of the 2000s.

The woefully underfunded parole system fell in line with the jail-first agenda. Parole officers, who were buried under massive caseloads, sent parolees back inside for technical violations, like failing drug tests, missing curfew or socializing with friends they had been forbidden to see. With nearly five million people in the nation under supervision — more than twice the number housed in prisons and jails — the parole and probation systems have become what corrections researchers now describe as a significant driver of recidivism.