The improvement of each treatment group,
given the absence of a no-treatment control condition, might
well be due to such influences as history, maturation, repeated
testing, and other threats to internal validity Our previous
work at the Child Conduct Clinic using the same recruitment
and screening criteria and attention-placebo and alternative
comparison groups (relationship therapy) has resulted in little
or no change over the course of treatment or follow-up without
a specific training regimen (Kazdin et al, 1987a, 1987b, 1989).
Nevertheless, previous demonstrations of no change for control
and alternative comparison conditions cannot rule out threats
to internal validity in the present study