In the present study, we examined both intra-individual growth, modeled at level-1 as a function of parental knowledge as a time-varying covariate, and inter-individual growth of the level-1 intercept (Π0i) and linear slope (Π12i) modeled as a function of parental knowledge averaged across all three time points, gender, and grade at level-2. Modeling parental knowledge as both a time-varying covariate and as a mean of the three time points allows: (a) examination of within individual changes in substance use as a function of changes in parental knowledge, and (b) examination of differences between individuals in substance use rates as a function of mean levels of parental knowledge, which is a proxy for a more stable estimate of parenting. Previous researchers have demonstrated that examining development from multiple standpoints is important as these results may vary depending on if the focus is on change or stability in parenting (Forehand & Jones, 2002; Way & Greene, 2006)
