THE SUBJECTS WERE 500 CHILDREN, 400 MALE AND 100 FEMALE, WHO WERE STUDIED AT THE JUDGE BAKER FOUNDATION OF BOSTON, MASSACHUSETTS, AND PLACED ON PROBATION IN THE JUVENILE COURT OF BOSTON. INTERVIEWS WERE BEGUN JANUARY 1, 1924 AND WERE RESUMED JANUARY 1, 1929, AFTER AT LEAST A 5-YEAR PROBATIONARY PERIOD HAD PASSED. THE RESULTS OF THIS STUDY ARE USED TO UNDERSTAND THE CAUSES OF DELINQUENCY AND RECOMMEND WAYS TO DEAL WITH THOSE CAUSES WHICH ARE MODIFIABLE. PROBATION AND THE ROLE OF THE PROBATION OFFICER ARE DEFINED. PRINCIPLES OF PROBATION TREATMENT ARE OUTLINED, AND THE NECESSITY FOR CONSTANT CRITICAL EVALUATION OF THE METHODOLOGY IS STRESSED. CHAPTERS SPECIFICALLY ADDRESS THE DELINQUENTS' PROBLEMS; THEIR HOME LIFE AND THE RELATION BETWEEN PROBATION AND THEIR PHYSICAL AND MENTAL HEALTH, TYPES OF COMPANIONS, FORMS OF RECREATION, WORK HABITS, AND EDUCATION. A CHAPTER ON THE OUTCOME OF THE PROBATIONS AND CONCLUSIONS IS INCLUDED. A MAJOR CONCLUSION IS THAT THE OUTCOME OF PROBATION IS NOT RELATED TO THE TYPE OFFENSE, BUT RATHER TO THE LENGTH OF TIME THE OFFENDER HAS BEEN CONSCIOUSLY VIOLATING SOCIAL STANDARDS. WHERE THE CHILD'S HOME AND NEIGHBORHOOD SITUATION IS INADEQUATE, THE THREE TYPES OF TREATMENT WERE: (1) SENDING THE CHILD AWAY FROM HOME, A LAST RESORT; (2) PERSUADING THE FAMILY TO MOVE TO A NEIGHBORHOOD WITH HIGHER STANDARDS AND LESS DANGERS; AND (3) CASEWORK ON THE FAMILY RESULTING IN MEDICAL CARE, PSYCHOTHERAPY OR EVEN RECREATION AT A CAMP. CHANGE OF COMPANIONS BY A DELINQUENT INCREASED SUCCESS IN PROBATION. GETTING DELINQUENTS BACK INTO SCHOOL OR INTO A JOB ALSO INCREASED PROBATION SUCCESS. GUIDELINES FOR PREVENTING DELINQUENCY ARE OFFERED. A LIST OF TABLES, A SUPPLEMENTARY LIST OF TABLES AND GRAPHS, A BIBLIOGRAPHY, INDEX, AND APPENDIXES ARE INCLUDED. (RBS)