The objective of this research was to evaluate the effectiveness of a behavioral intervention program on the reduction of disruptive behavior, and the increase of prosocial behavior in a classroom context. In order to do so, the class teacher received training in the use of a series of behavior modification techniques (namely instructions, verbal praise and token economy). After training the teacher, she implemented the procedures in a first year class of secondary school that presented severe behavioral problems. A reversal design ABAB was used in order to evaluate the performance of the teacher in the implementation of the behavioral modification techniques taught and to evaluate the effect of these techniques on the group. Results indicated that the teacher was able to implement appropriately all the behavior modification techniques. The implemented procedures were in turn able to generate the desired changes in student behavior during class time.