This article reports a study aiming to understand the classroom practice of four grade 7 science teachers following an in-service teacher-development programme. Such studies are needed to contribute to knowledge about the effectiveness of professional development programmes. Clarke and Hollingsworth’s model of professional growth was used as a theoretical framework. Data were collected by means of interviews, lesson observations and document analysis. It was found that each teacher experienced professional growth in a personalised way, such as increased confidence, improved content knowledge, teaching strategies, practical skills, and valuing professional collaboration. All the teachers reported that their classroom practices have improved. Lesson observations revealed that three of the four teachers were enthusiastic and engaged their learners in practical work. Challenges such as lack of resources, poor language skills, and lack of higher cognitive levels in activities and questions were observed for all the teachers. An adapted model of professional growth has been proposed to represent the professional development of science teachers in poorly resourced schools.