Using evidence-based practices in the juvenile justice system reduces delinquency and avoids costs. Those of us in the field hear this regularly – but it can be hard to see their impact on a day-to-day basis.
How do we know they work? Let's start at the beginning. What we commonly refer to as "evidence-based practices" in the juvenile justice field are based on over 40 years of research regarding what works to reduce juvenile crime. Unlike studies that look at single programs, this research looked at over a hundred studies and found what consistently worked to reduce crime versus what consistently made crime worse. 
It showed that services that combine juvenile corrections (detention, probation, community service, restitution to victims, etc.) with treatment that address dynamic risk areas have a significant impact on reducing crime. Treatment includes alcohol and other drug treatment, school support, anger management, family counseling, mental health services, etc. The treatment aspect must include skill-building, so youth and families leave the system better able to live productive lives. The intensity of treatment must be matched to the youth’s risk level.
All youth in the system should receive this mix of sanctions and treatment, but low-risk youth should receive less intensive services and high-risk youth should receive more intensive services. (Research indicates that intensive services for lower risk youth can actually increase delinquency.)
This approach can literally turn the tide on delinquency. I will focus on the high-risk offenders to illustrate this point. In Oregon, where I work, we define "chronic juvenile offenders" as youth who commit three or more new criminal offenses during a follow-up period. A 2006 Oregon study of chronic juvenile offenders found that the percent of youth who became chronic dropped from 7.2 percent in 2001 to 6.2 percent in 2006.
So What? A lot of resources go toward crime reduction. What difference does it make to reduce the chronic group by one percentage point? It makes a huge difference. If Oregon had one percent fewer chronic offenders (7.2 percent to 6.2 percent) in a single year, there would have been 2,000 fewer crimes, with over $22 million in avoided costs.
The cost avoidance study has been conducted for each county in Oregon. For example, Douglas County has strategically implemented evidence-based practices over the last several years. Out of a sample of 699 juvenile offenders with a criminal referral, 9.6 percent were chronic offenders in 2001; a rate that dropped to 5.9 percent in 2008.
What would have been the impact in 2001 if the chronic youth offender group rate in Douglas County had been the same as it experienced in 2008? There would have been 284 fewer crimes, for a cost avoidance of $3,165,427. 
Reducing the percentage of youth who become chronic offenders even by a small amount significantly reduces crime in local communities and yields substantial cost avoidance. This occurs because the chronic group is so criminally active that even a small reduction creates very positive outcomes.
The cost avoidance calculation is based on:
a) an average cost to victims established by a national study;
b) costs to the juvenile justice system including personnel, programs, utilities, training, supplies, etc.;
c) costs to law enforcement including making arrests and processing of juvenile crimes; and
d) prosecution, defense, and court costs.
Unlike “cost savings” -- which suggests funds sitting in a bank -- cost avoidance is related to the cost of each criminal referral and what is “avoided” by reducing delinquency.
Investing in evidence-based practices is the best way to achieve significant cuts in crime and their associated costs. All we have to do is look at the data.
The above story is reprinted with permission from Reclaiming Futures, a national initiative working to improve alcohol and drug treatment outcomes for youth in the juvenile justice system.
 Latessa, Edward J 2004. "From Theory to Practice: What Works in Reducing Recidivism?" State of Crime and Justice in Ohio, pp. 170-171.
 Wagner, Linda 2010. "The Cost Avoidance Model," Douglas County Juvenile Department 4th Annual Report Card To The Community: Fiscal Year 2009-2010, p 5.