This explorative field study examined the mediating role of self-regulated learning (SRL) in the relationship between the personality trait of conscientiousness, SRL, and science achievement in a sample of junior high school students. Over the course of an entire academic year, data on enacted SRL were collected each week for 52 eighth-grade students in the context of an inquiry-based ecology project. Data were also collected on personality traits, self-reported study strategies, science project achievement, and grade point average. Findings show significant relationships between conscientiousness, SRL, and achievement. As hypothesized, conscientiousness was shown to significantly impact academic achievement in the inquiry-based course, mediated by enacted SRL. (Contains 3 tables and 1 figure.)