Here is a study released by the Centers for Disease Control and Prevention in 2007.
"Available evidence indicates that transfer to the adult criminal justice system typically increases rather than decreases rates of violence among transferred youth. Available evidence was insufficient to determine the effect of transfer laws and policies on levels of violent crime in the overall juvenile population. On the basis of these findings, the Task Force recommends against laws or policies facilitating the transfer of juveniles to the adult criminal justice system for the purpose of reducing violence."Read the study and its recommendations here.