This paper reports on an assessment of knowledge of SDL in primary (elementary) South Australian school students, fifty-six of whom were assessed to be high reasoning. The goals of the study were to identify the effectiveness of teaching and assessing knowledge of Self-Directed Learning (SDL) in high reasoning students, investigate whether there were differences in students' knowledge of SDL related to reasoning, and to identify the influence of engagement on high reasoning students' knowledge of SDL. The students were taught about SDL in four class lessons. Partial Least Squares path analysis showed that there were significant (negative) differences in high reasoning students' development of knowledge of SDL. This indicates that high reasoning students were more engaged and had an indirect gain of knowledge of SDL as a result of the teaching intervention suggesting that high reasoning students could become more self-directing if they are highly engaged in classroom activities about SDL. (Contains 5 tables and 1 figure.)