Final answer:
The probable source of this behavior is modeling, where the adolescent imitates the aggressive behavior they have witnessed in their dysfunctional family.
Step-by-step explanation:
According to the principles of behavioral therapy, the probable source of this behavior in the adolescent is modeling. Modeling refers to the process of learning behavior by observing others. In this case, the adolescent is likely mimicking the aggressive behavior they have witnessed in their dysfunctional family. By observing and imitating the physical and verbal abuse prevalent in their family, the adolescent is displaying similar behavior towards their classmates at school.