The purposes of this study were to: 1) determine in what ways incorporating active engagement into a traditional lecture chemistry course contributed to students' science identity and their motivation to learn the science, and 2) determine how the development of a science identity could be measured through the use of a quantitative instrument and tracked over time. Students took a 13-item science identity questionnaire, designed and validated as a part of the current study, and Glynn and Koballa Jr.'s (2006) 30-item motivation questionnaire three times (pre, mid and post) over a 10-week term. The science identity questionnaire was developed to measure aspects of a students' science identity using a conceptual framework that situated identity as both individually and socially constructed. The theorectical framework that guided the design of the instrument involved self-concept, presented self, and recognition by others that interact within the context of the social environment of college to affect development of student identity. The assumption was made that all students enter into college with some measure of a science identity. The participants (n=1246) were enrolled at a large, research university in the Pacific Northwest in one of two undergraduate, general chemistry courses that were taught using either an experimental active engagement section or using a traditional lecture method. Students in the experimental section (n=113) were predicted to show higher intrinsic motivation, self-efficacy, and self-determination in learning chemistry and to show maintenance or development of a science identity over time compared to their counterparts (n=634) who were not receiving the treatment. Students in a general chemistry course for engineers (n=500) were used as a positive control and hypothesized to have a well-developed science identity that would remain stable. Results of the science identity questionnaire showed that students’ science identity could be grouped into several categories using a cluster analysis. Open-ended interviews were used to in conjunction with the survey data to verify these categories. Students' science identity ranged on a continuum from low to high, that could be monitored over time. The positive control group (the engineers) exhibited a higher science identity than either the experimental group or its counterpart, and served as a reference standard for measuring science identity. The experimental group reported an initial lower level of science identity than the positive control group and this difference was significant. Over the course of the term, the experimental group reported a science identity that ceased to be significantly different from the positive control group, suggesting a similarity in science identity between the two groups. The results of the motivation survey showed several aspects of motivation that changed over time, with no significant differences seen in total motivation. Significant differences between the two groups were seen in self-efficacy, extrinsic motivation, and self-determination. This study provides a quantitative reference standard for science identity and a novel instrument for measuring and tracking development of a students' science identity.