This article describes the development and validation of the Self-directed Learning Scales (SLS) using data from 14,846 secondary students. Self-directed learning refers to a process whereby the learner consciously and actively directs his/her actions in the learning process. The SLS comprised a battery of subscales measuring students' goal setting, planning, academic motivation, academic self-efficacy, inquiry and information processing, strategic help-seeking, management of learning resources, and self-monitoring. Rasch analysis following factor analyses provided evidence in support of the validity of SLS for use with secondary students. Two original subscales were merged with other subscales on the basis of the analyses, resulting in 19 subscales with strong psychometric properties in the Self-directed Learning Scales.