In looking to answer my own question, I found a couple of relevant tidbits:
From http://www.bestweb.net/~cureny/educatn.htm (any emphasis added is mine)
A 1994 report by Miles Harer, (“Recidivism Among Federal Prison Releases in 1987,” Fed. Bur. of Prisons, Office of Research and Evaluation, 1994) concluded that recidivism rates were inversely related to educational program participation while in prison. The more educational programs successfully completed for each 6 months confined, the lower the recidivism rate.
A report of the Adult Probation Dept. of the Superior Court, Pima County, Arizona concludes that offenders given literacy training in 1994 had a lower new felony arrest rate (23%) compared to a control group (40%). Offenders given a GED education in 1994 had a lower new felony arrest rate (15%) than a control group (40%). The Bureau of Justice Statistics reports a 43% recidivism rate for adult offenders on probation nationally in 1994 (based on felony arrests).(from “The Impact of Correctional Education on Recidivism, 1988-1994” Office of Correctional Education, U.S. Dept of Ed.)
A 1994 State of Texas report (Tracy and Johnson, Windham School System) found that the recidivism rate for those who received both a GED certificate and completed a vocational trade was over 20% lower than for those who did not reach either milestone. (ibid))
That Texas report also showed that two years after release, the overall recidivism rate for degree holders was a low 12%, and inversely differentiated by type of degree: associate, 13.7%; baccalaureate, 5.6%; masters, 0%.
A 1991 study by the NY State Dept. of Correctional Services showed that three years after earning a college degree in inmate college programs, offenders were significantly less likely to recidivate (26%) than non-degreed inmates (45%). (ibid)
In a letter to the Utah State Legislature, Jeffrey Galli, of the Utah State Office Of Education (and formerly a prison warden for 22 years) writes: "Data received from independent evaluators indicate that Project Horizon (a comprehensive education and training program) reduces recidivism from 20 % to as much as 26%. (ref.: KT Adult Learning Quarterly,winter 1996).
A 1983 study at Folsom Prison in California showed that none of the prisoners there who earned bachelor’s degrees recidivated, compared to the 55 percent recidivism rate of the rest of the prisoners released (Lawyer and Dertinger, “Back to School or Back to Jail,” ABA Criminal Justice, Winter 1993, p. 21).
Rearrest of young parolees has also been shown to be related to the amount of prior education. Based on a sample of parolees between the ages of 17 and 22, who were paroled from prisons in 22 states in 1978: an estimated 48% of the parolees who had attended some college were rearrested, compared to 61% of the high school graduates, and 71% of those who had not completed high school. (Bu. of Justice Statustics Special Report, “Recidivism of Young Parolees.”)
I’ll try to find more later, but those statistics, if significant, seem to argue heavily in favor of rehabilitative and educational efforts.