Walker cites the National Academy of Sciences stating that rehabilitation is “any planned intervention that reduces an offender's subsequent criminal activity (Walker 251). » Walker divides rehabilitation models into two groups, new and old. New groups that Walker says might have some positive hope are reentry programs and drug courts. Former groups include probation, parole, and other reentry programs. Worrall has a similar definition of rehabilitation, stating that “rehabilitation consists of a planned intervention intended to change behavior (Worrall 40). He similarly evaluates several of these programs and reaches conclusions similar to Walker's. Drug courts are specialized courts that focus on drug abuse. Typically, offenders have the opportunity to avoid jail or prison time if they successfully complete a drug treatment program (Walker 275). Walker believes that drug courts, when well managed and carefully designed, show promise and could reduce recidivism (Walker 277). Worrall reached similar conclusions, saying that although much of the research on the effectiveness of drug courts has suffered from design limitations, it has shown a reduction in recidivism (Worrall 168). Reentry programs attempt to take a new look at returning prisoners to society after revamped education and counseling programs (Walker 363). Unfortunately, there is not much evidence that these programs reduce recidivism rates (Walker 363). Walker concludes that the evidence is inconclusive, that the programs are in their early stages, and that additional research is needed because of the current crisis of releasing so many prisoners (Walker 363). Probation is when offenders are monitored and treated in the community rather than in a correctional setting (Walker 255). Walker believes probation is necessary and appropriate for many offenders. However, he also claims that most probation programs fail and that there is no evidence that one probation program is more effective than another (Walker 257). This is for several reasons: initially, probationers receive largely no treatment, only supervision, and even this supervision is often very intermittent, and there are problems controlling the quality of treatment and supervision ( Walker 256). Parole is the most classic example of a social reentry program, which involves the early release of a prisoner into the community, usually under some type of treatment and supervision, similar to probation (Walker 257) . In addition to attempting to rehabilitate offenders, parole also serves several other purposes, such as incentivizing prisoners to behave well, giving the correctional system a tool to control prisoners, and serving as a means of dealing with prison overcrowding ( Walker 257).