Parental monitoring and knowledge of their teens' activities might enable parents to keep teens safe, reducing the risk of potentially traumatic events. This paper investigated that possibility using a large, nationwide sample of 11,880 early adolescent teens followed longitudinally from ages 10-11 to 13-14 years old. At annual assessments, teens completed measures of parental monitoring/knowledge and of potentially traumatic events. Data were analyzed using multilevel models to separate between- and within-family associations. Because within-family associations cannot be explained by the many systematic differences between families with low vs. high monitoring, they comprise more rigorous evidence of a potential causal relationship. We tested both concurrent associations between monitoring/knowledge and PTEs and prospective associations over 12 months. At the between-family level, every tested association was significant (p <
.001): greater monitoring and/or knowledge predicted fewer PTEs. However, at the within-family level, few associations were significant. Greater knowledge (p = 0.005) or combined monitoring/knowledge (p = 0.01) predicted fewer PTEs concurrently, but greater monitoring alone did not (p = 0.14). No prospective within-family associations were statistically significant. We replicated this pattern of findings in a different set of observations from the same sample, using different measures of each construct. We conclude that most of the apparent association between parental monitoring/knowledge and PTEs is explained by confounding factors, rather than a causal relationship. However, we found some evidence supporting a causal link in models of concurrent associations, suggesting any causal relationship between monitoring/knowledge and PTEs may unfold over shorter timescales.