In the juvenile justice sytem, psychologists are expected to predict which defendants are dangerous and which will be delinquent in the future (the assessment function) and to reform offenders (the treatment function). Ethical problems are compounded by the great deal of discretion permitted to criminal justice system officials. Constraints on thinking and acting encountered by psychologists can be divided into three categories: (1) dominant societal values such as the premise that the individual juvenile is not only the culprit but also the proper focus of change, (2) officialdom, or the influence of funding agencies on the type and formulation of research problems, and (3) paradigm constraints or unconscious acceptance by social scientists of popular structures of reasoning (e.g., a traditional 'cause and effect' model). Some of the things psychologists should do to overcome the constraints include recognition that their work always requires them to take value stands and taking them into account, rejection of entrenched paradigms, and open acknowledgement of limits on their competence. Tabular data, notes, and over 100 references are included.