Science teachers are increasingly encouraged to critically engage their students with scientific knowledge and expertise, with the expectation that such instructional practices will support the development of scientific literacy (SL). Drawing on Bildung framework, this qualitative study was conducted in Tanzania to explore how science teachers' classroom practices facilitate the development of students' SL. Data were collected through semi-structured interviews and non-participant classroom observations with science teachers and students from six secondary schools. The study has identified five instructional practices that were used to support students' development of SL, namely guided reading, code-switching, educational print and visual aids, science experiments, and science projects. While there is evidence that the instructional practices used provided opportunities for students to contribute their thinking, experience and understanding to the science learning, the instructional practices were mostly print-based, paper-based and teacher-led, resulting in little engagement in active scientific thinking and literacy learning. Overall, the knowledge base developed by this study is of practical use to science teachers and educators in making decisions about appropriate instructional practices and what should be the regular focus of pre-service teacher education and professional development programs.