Using growth curves to examine timing of school-based substance use prevention in elementary versus middle school among Mexican heritage youth

Few studies have directly compared substance use interventions starting in elementary school versus middle school. To gauge any advantages of early intervention, this study reports on a randomized controlled trial comparing students who received the keepin' it REAL model prevention program in 5th grade, 7th grade, both, and in neither of those grades. Data come from students recruited in 5th grade from 30 elementary schools in Phoenix, AZ and tracked through the end of 8th grade. This analysis utilized 1,670 Mexican American youth completing questionnaires at baseline and 5 post-tests through 8th grade. To estimate treatment effects we used growth curve models that modeled changes in the frequency of last 30 day use of each of four substances (alcohol, cigarettes, marijuana, inhalants). Results indicated that intervention in 7th grade was effective in reducing the growth trajectory of use of all four substances, and intervention in both 5th and 7th grades showed similar desirable effects but only for marijuana and inhalants. Students receiving the intervention in 5th grade only were statistically indistinguishable from controls in the models for all substances. Results confirmed that the original model program developed to be delivered only in 7th grade was effective in restraining use of substances. Intervening in only elementary school was ineffective, and intervening in both elementary and middle school showed fewer desirable effects than a single intervention in 7th grade. Drug resistance skills training may not be developmentally appropriate for 5th grade students and therefore should be more substantially adapted for them.