The purpose of this study was to obtain a better understanding of the professional learning needs of Tanzanian science teachers who were recruited using an alternative route approach to teacher recruitment and to seek ways to address these needs. The alternative route to teacher recruitment usually refers (but not always) to the enlistment of university graduates, who are trained in a non-accredited teacher education programme, and then licensed or certified to teach in schools. In Tanzania teachers trained in this way are referred to as ‘licensed teachers’. This study first identified the licensed teachers’ professional learning needs in relation to pedagogical content knowledge (PCK) by examining their effectiveness in using learner-centred teaching methods in the classroom. The findings from this first phase of the investigation revealed that the licensed science teachers rarely used learner-centred strategies and their PCK was underdeveloped in this area. In the second phase of the study a professional development intervention (PDI) was developed and implemented to enhance the licensed science teachers’ PCK and improve their classroom teaching practices. This study used a multiple case study approach underpinned by an interpretive research paradigm. The study adopted the situativity theory to inform the professional development intervention, with the view that teachers’ learning and knowing are situated in and influenced by the physical and social context and participation in authentic activity as a community of learners. The participants of this study were six licensed teachers, twenty four students and five education officials. Data were collected from multiple sources such as classroom observations, one-to-one semi-structured interviews, focus group discussions, documentary reviews and teachers’ reflective notes. The data were analysed thematically using the five components of PCK identified by Magnusson, Krajcik, and Borko (1999), as the analytical framework. The results from the first phase of investigation showed that the licensed science teachers had underdeveloped PCK and did not use/understand learner-centred teaching methods. Instead their classroom teaching practices were dominated by teacher-centred teaching methods and they lacked the skills of preparing learner-centred science lessons. Also tests and examinations prepared by the licensed science teachers were found to be mostly testing the lower levels of Bloom’s knowledge taxonomy, that is, knowledge, comprehension and application, with few items relating to analysis. The evaluation of the PDI indicated that it had a positive impact on licensed science teachers’ PCK, with the licensed teachers showing improved classroom teaching practices after the PDI. Students’ learning was enhanced as a direct result of licensed science teachers’ improvement in their ability to design and teach lesson using learner-centred teaching methods. This study has implications for teacher education practice and students’ learning in countries using an alternative approach to teacher recruitment and for educational research. This thesis offers suggestions for reform in teacher education institutions, policy and practice and for further research into how to improve this form of alternative route to teacher recruitment. The most significant of these suggestions is the setting up of PLCs of teachers with on-going expert support and school leadership (headmasters/mistresses, district educational officers) involvement. This on-site structure for sustained, supported professional learning offers a way forward for improving PCK of many untrained licensed teachers currently working in Tanzanian rural community secondary schools. The thesis concludes that unqualified licensed science teachers working in schools need school-based professional development support to enhance their underdeveloped PCK, since students taught by licensed teachers are unlikely to be receiving the levels of knowledge and skills potentially needed to compete in the global economy.