The present study examined the relation between adolescent substance use and young adult educational attainment, testing whether adolescent substance use serves as a marker or a mediator of a broad matrix of risk factors for lowered educational attainment in young adulthood. The findings provide evidence for both the marker and the mediator hypotheses, and identify multiple pathways to higher educational attainment.
As expected, parental education predicted both the pursuit of higher education and successful degree completion, in part via adolescent reading achievement, reflecting the intergenerational transmission of educational attainment. Adolescents with more educated parents are likely to be in family contexts that value, encourage and model academic pursuits, have economic resources to provide educational opportunities [14
], as well as have heritable individual differences in academic abilities. Thus, one basic pathway to young adult educational attainment reflects the intergenerational transmission of higher educational attainment through early adolescent academic achievement.
The question of central interest was how adolescent substance use fits into the larger matrix of behavioral, familial, cognitive and self-regulatory influences on higher educational attainment. Initial models showed that after adjusting for the effects of parental education and adolescent reading achievement, there were significant effects of mean levels and growth in adolescent substance use on both college attendance (for drug use) and degree completion (for alcohol and drug use). This is consistent with previous research [6
]. However, the effects of adolescent substance use were largely eliminated when their antecedent risk factors were entered into the model. Thus, to some extent, adolescent substance use seems to serve as a marker for a larger constellation of risk factors, identifying those adolescents who are at risk but not playing a causal role. These findings are similar to those of Fergusson & Horwood [8
], who found that the effects of substance use on adolescent psychosocial outcomes were largely eliminated when prior risk factors were accounted for in the model [24
Although many of the effects of adolescent substance use on educational attainment were eliminated after considering antecedent risk factors, a significant relation remained between growth over time in adolescent drug use and successful degree completion. This finding suggests that acceleration in adolescent drug use is not simply a marker for other risk factors in terms of its effects on finishing a college degree. Thus differentiating between mean levels of use and change in use over time is important in understanding the effects of substance use during adolescence.
In fact, growth in adolescent drug use significantly mediated the effects of externalizing behaviors on degree completion. Baumrind & Moselle [13
] theorized that adolescent substance use impedes the development of self-regulatory and coping skills. Externalizing adolescents, who are poorly regulated, are also more likely to escalate their drug use, which may further impede the development of the social and behavioral competencies that are necessary for success in higher education.
These results were found for escalation over time in drug use but not alcohol use, suggesting that there are important differences in the effects of growth in alcohol versus drug use on educational outcomes in young adulthood. For example, this finding may reflect a difference in the prevalence and relative deviance of adolescent alcohol use compared to illegal drug use [26
]. Indeed, college students use alcohol at higher levels than do their same-age peers who do not attend college [47
], but illicit drug use (particularly drugs other than marijuana) is more prevalent among non-college attending peers than among college students [49
]. Therefore, adolescents who escalate illegal drug use over time may become part of a deviant peer network whose values and activities are less compatible with the academic demands and social climate of higher education. Indeed, the drug-using adolescents in our sample also were the heaviest drinkers, suggesting that their pattern of substance use was the least normative, particularly for college students, and that the effects of drug use in the current study may also include the comorbid effects of alcohol and drug use. Additionally, these differential findings for alcohol and drug use may reflect higher behavioral under-control or disinhibition among adolescents who use illegal drugs versus just alcohol [31
The effects of growth in adolescent drug use were specific to degree completion, rather than to entry into post-high school education. Additionally, other significant predictors of degree completion (such as externalizing symptoms) were not related directly to college attendance, which was predicted only by parent education and adolescent academic achievement. In the current study, college attendance was defined with the highest level of education completed being ‘some college or better’. This could reflect a spectrum of possibilities from enrolling full-time at a highly selective private university or taking a few courses part time at a community college. Thus, different findings might be obtained if the definition of ‘college’ is narrowed to include only 4-year colleges or full-time students. However, considering that only 59.6% of college students attend college full time [51
], the data from our prospective community sample may provide a more realistic picture of the nature of college attendance. Our findings may also suggest that selection into college may be driven primarily by educational factors, but success in college may be influenced more strongly by behavioral factors. Many studies examine a single marker of educational attainment [3
] or a continuous measure of educational attainment [7
]. However, the current findings suggest that the effects of substance use may not be consistent across levels of educational attainment and that the barriers to performing well in and graduating from high school probably differ from barriers to being able to perform successfully in and graduate from college.
The current findings demonstrate the importance of considering a broader matrix of risk factors when examining the effects of adolescent substance use on later adult outcomes. The ‘marker or mediator’ hypothesis also has important implications for prevention research. For example, one long-term benefit of successful drug use prevention might be an increased likelihood of completing a college degree. However, our models also suggest that targeting externalizing behaviors in adolescence may have wider benefits on academic performance, both during and after high school. In a broader sense, the ‘marker or mediator’ hypothesis can be used to identify clearly potentially modifiable mediators to target for intervention by studying the outcomes of risk behaviors in light of the developmental processes that produce them, thus providing a means of identifying the most profitable targets for intervention.
In spite of the importance of the present findings, there are also limitations of our study that should be noted. First, we do not have data on the types of colleges our participants’ attended or the reason for not completing a college degree by Time 5. This limits our ability to interpret the lack of relation between substance use and college attendance. Additionally, we examined consumption of alcohol and drug use, rather than substance use consequences or disorders, both of which may be more strongly related to high school academic achievement and college attendance. We examined only one indicator of early school success (reading achievement as measured by a standardized reading test) in our models. Future studies should include more comprehensive assessments of adolescent school performance, such as behavioral reports and grades.
In summary, we found that substance use during adolescence serves as a marker of a broader spectrum of problem behaviors which reduce academic achievement during adolescence and also impact later selection into and success in college. However, growth in drug use had specific direct effects on completing a college degree, accounting partially for the effects of externalizing symptoms on degree completion and suggesting that those adolescents whose drug use accelerates during adolescence experience additional risk for poor educational attainment due to their illicit use of drugs.