This paper outlines a University-School District partnership with the intent to increase the number of middle grades mathematics and science teachers. This externally funded initiative includes onsite, authentically situated professional development for pre- and in-service teachers at three different urban, low-socioeconomic schools with a majority Hispanic population of students. Program objectives include increasing mathematics and science content knowledge, increasing self-efficacy in teaching math and science, building and incorporating a success-driven school culture and infrastructure to increase student performance in a well-articulated, scalable and transformable model. Program components include site based common planning times, STEM Thursdays where science and mathematics lessons are practiced and refined, authentic summer research opportunities for pre- and in-service teachers to work with scientists and university faculty, teacher certification workshops and a mentoring model that includes program graduates and pre-service teachers. First year results show that the program had a positive impact on the teachers' self-efficacy and outcome expectancy as their scores significantly increased after participation in the project. Key elements in the model included (1) a strong partnership between a school district and institution of higher education, (2) a unique collaboration between mathematics and science educators and scientists, pre-and in-service teachers, (3) a professional development and mentoring program designed around the school district's adopted course of study and the NSES, (4) the integration of community resources, (5) a partnership with preservice and inservice teachers and district administrators with science and mathematics higher education faculty, (6) the development of teacher leaders, and (7) a comprehensive evaluation program.