The study investigates the effects of a professional development strategy which focuses on the use of a contextually appropriate analogy on the development of isiXhosa speaking learners‟ conceptual understanding in direct current electric circuits, where the language of instruction is English. An action research design was implemented, using three data collection cycles to document the research journey. The sample comprised of two Grade 8 and 9 classes drawn (with their respective Natural Sciences teachers) from two neighbouring, township schools in Nelson Mandela Metropolitan Municipal area. Qualitative data were generated from interviews and classroom observation of the two science teachers (a qualified and an unqualified teacher) and learners, over a span of two years. Thematic data analysis revealed that ESL learners have alternative conceptions in simple circuits and teachers have no knowledge about analogies that can be used to teach simple circuits. A professional development was designed as a strategy, targeting the development of the Science Content Knowledge (SCK) and Topic Specific Content Pedagogic Content Knowledge (TPSCK) of the teachers. Data analysis of the professional development initiative (PDI) suggests that the teachers developed increased knowledge of concepts and teaching strategies used in teaching simple circuits, selected a contextually appropriate analogy and taught a lesson in simple circuits using the selected analogy. Analysis of learners‟ post-test results suggests that the implementation of the selected analogy developed their conceptual understanding as more learners developed the correct, scientific model of reasoning. The results of the study suggest that when teachers are given support by being exposed to professional development; their scientific reasoning, confidence and classroom climate become more positive and learners‟ conceptual understanding improves.