The purpose of this study is to understand how secondary science teachers conceptualize student science identity and the impacts of this thinking on actions and planning with teaching. Research on how science identity impacts college students is more robust while little research looks at the impacts of secondary science teachers on science identity. Previous research shows that recognition by the science community as well incorporation of home cultures is important in the development of student science identity. Critical incident theory in phenomenology was used to interview participants over time to gain greater understanding of their thinking about student science identity. Results from these interviews found that the participants were focused on the identities of their students both explicitly and implicitly. This knowledge of their students allowed the participants to make choices in their instruction and planning that were focused on students' cultures, interests, needs, and experiences outside of the classroom. Findings also showed instructional choices around grouping, modeling, grading, and student voice that were consistently used by the participants that could impact the development of student science identity. Despite a focus on who their students were, the participants did not explicitly discuss student science identity. This study shares important considerations for teachers and educational leaders for developing classrooms that build student science identity. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]