In 2002, the Tanzanian government launched the Primary Education Development Plan in order to meet its commitments to global Education For All targets and the Millennium Development Goals. Although Tanzania has made great strides in improving access to primary education, achievements in learning outcomes have been slow to come, which has prompted concerns about the quality of Tanzania's teaching force. Research has broadly positioned teachers as either the cause of poor education quality (through commentary on teachers' 'deficient' behaviours, such as absenteeism, rote-teaching, and withholding content); or the victims of a flawed system, which has been demonstrated through expositions of teachers' impoverished working and living conditions. This thesis aims to draw these polarised views together by using the Capability Approach supplemented with a Critical Realist theory of causation, to investigate the relationship between teachers' conditions of service and their criticised behaviours. The rationale for using the Capability Approach lies in its ability to offer an alternative analytical space in which to understand teacher's well-being, as it elucidates how environmental, social and personal conditions may constrain the 'beings and doings' that people value. This form of constrained well-being can be linked to teachers' 'deficient' performance by locating it within a Critical Realist theory of causation; which provides ontologically grounded, holistic accounts of the underlying mechanisms, structures and tendencies that generate empirical behaviour. The Capability Approach I Critical Realist framework that this thesis develops will be contextualised with qualitative data collected from three Tanzanian primary schools from June - November 201 O; and analyses will demonstrate how teachers' criticised actions are often a result of their constrained capabilities. By understanding teachers in this way, holistic and nuanced explanations for various practices and behaviours can be made, which has the potential to enhance future practice and policy regarding teachers in Tanzania.