The Development of Internalizing and Externalizing Symptoms in Middle Childhood and Substance Use Prior to Middle School Entry

Abstract

Substance use disorders are considered externalizing disorders, defined by anti-social and impulsive behavior, as opposed to internalizing disorders, defined by anxious and depressive thinking; however, that strict binary is increasingly untenable. In this dissertation, I evaluate the co-development of internalizing and externalizing symptoms during middle childhood and find both internalizing and externalizing pathways to substance use among a majority Black and Hispanic, predominantly low-income group of children in New York City public elementary schools. I employ statistical methods that gradually shift the analysis from a variable-centered perspective to a person-centered perspective to identify the developmental warning signs of early substance use. I discuss the implications of the findings for substance use prevention programs, which in the United States primarily take place in public schools.

In Study One, I find three pathways to substance use, including an internalizing pathway, an externalizing pathway, and an independent pathway through social failure and disengagement from school. Restrictive parenting and challenges with emotion regulation serve as the developmental starting point for each pathway. Children who are socially competent and engaged at school may be protected from early substance use, regardless of their clinical symptoms.

In Study Two, I find that children with early and growing externalizing symptoms are at greater risk for early substance use. Children with higher-than-expected internalizing symptoms, given their average internalizing symptom development, tend to have higher externalizing symptoms later on and are at greater risk for early substance use. The findings suggest that preventing and treating both externalizing and internalizing symptoms in elementary school may help reduce early substance use.

In Study Three I find that children with comorbid, persistently high internalizing symptoms and growing externalizing symptoms are at greatest risk for substance use. Children with high and growing externalizing symptoms but not internalizing symptoms are at similarly high risk for early substance use. Children with moderate internalizing symptoms, who initially exhibit high and growing externalizing symptoms that diminish over time, are at low risk for early substance use. The findings suggest that children with high and growing externalizing symptoms can recover during elementary school and have low risk for substance use.

Collectively, the studies in this dissertation provide support for a broader view of substance use, driven by both internalizing and externalizing symptoms. Universal prevention programs that promote emotion regulation, social competence, and school engagement in elementary school may help reduce risk for substance use before middle school, when rates of substance use rapidly increase. Targeted prevention programs may be effective by treating children with high and growing externalizing symptoms and persistently high internalizing symptoms, or children whose internalizing symptoms suddenly increase, in elementary school.