both tobacco and alcohol use. For example, there was a 61% reduction
in the annual rate of smoking (Eta-squared = .36), and a 25% reduction
in the annual rate of alcohol use (Eta-squared = .17).1
In addition, this study has several strengths that provide further support
for the validity of these findings. First, the study used a true experimental
design in which schools were randomly assigned to either
prevention or control conditions. This eliminated the potential of contamination
across conditions that would otherwise be present in a design
in which classes within the same school were assigned to experimental
conditions. Second, many prevention studies testing school-based
approaches have been criticized for failing to adequately control for the
observed correlations of individuals within assignment clusters (e.g.,
schools), which may inflate the Type I error rate (Murray et al., 1990). A
variety of methods exist for dealing with ICCs including either statistically
adjusting for school-level ICCs or conducting analysis on the cluster
(school) level using approaches similar to that used in the current
study. Other strengths of the current study include the use of developmentally
appropriate assessment instruments and data collection procedures
designed to enhance the validity of students’ self-reports.
At the same time, this study also has several limitations that should
be noted. First, the findings presented are from the immediate posttest
after a single year of intervention. Additional follow-up data are needed
to determine the longer-term durability of these prevention effects with
this population. Second, since this was a school-based study that relied
on students’ self-reports, the significant relationships among variables
may partly reflect shared method variance (all data was obtained by
self-report questionnaire). Third, in an effort to use measures that were
age-appropriate, some measures used fewer response options than in research
using similar measures with older populations. Moreover, only
some of the outcome measures used in this study were affected by the
intervention. Fourth, it is unclear whether these findings generalize to
populations different from that included in this study. For example, be- cause students who are absent during data collection are likely to be at
somewhat higher risk than those who provided pretest and posttest data,
it is unclear to what extent the findings of this study are applicable to
high-risk students. It is also unclear to what extent these findings are ap- plicable to different ethnic subgroups. Because the population included
in this study was racially/ethnically diverse, it is likely that this preven- tion approach is effective with multiple populations. However, neither
the design of the current study nor the sample size was adequate to em- pirically test the relative efficacy of this approach with the different
populations comprising this sample. Similarly, it was not possible to de- termine the relative efficacy of the prevention program by age or grade
14 JOURNAL OF CHILD & ADOLESCENT SUBSTANCE ABUSE
level. Additional research is needed to determine the extent to which
this prevention approach is effective with different populations as well
as to determine whether there were developmental differences in the efficacy
of the prevention program for the different age groups/grade levels
involved in the study.
The results of this study provide the first evidence for the effectiveness
of a comprehensive school-based prevention approach designed
for elementary school students that teaches substance use resistance
skills, normative education, personal self-management skills, and general
social skills. These results extend prior research with the LST approach
by demonstrating its effectiveness with a younger population.
This study is also important because it uses rigorous research methods
including a randomized control group design and data analysis methods
that adjusted for school-level intra-cluster correlations. Finally, this
study is important because prevention programs administered during elementary
school either alone or in combination with similar programs
during middle or junior high school offer the potential of producing a
greater impact on adolescent substance use.
Future research is needed to replicate the findings of this study and
determine the impact of this prevention approach on a wider array of
outcome measures. Research is also needed to determine the durability
of these prevention effects with longer-term follow-up assessments, the
impact of this prevention approach on high risk youth and other subgroups
of youth, and the extent to which these findings generalize to
other populations.
NOTE
1. The percent reductions in smoking and drinking were calculated by taking the
difference score in annual prevalence rates at the posttest assessment between the experimental
and contr