This document reports on a research study carried out in a rural public school in Colombia. The aim of the study was to identify the impact of a task-based teacher development program on three primary school teachers' teaching practices. To this effect, we used a survey, classroom observations, and semi-structured interviews before and after the implementation of the development program. We identified that teachers' perceptions, beliefs, and realities in their teaching practice influenced their performance, inside and outside the classroom. The results also showed that participants improved their teaching practices regarding the processes of lesson planning and materials design. They also improved their English language performance regarding pronunciation and vocabulary use.