Teaching is undoubtedly complex and the complexity of classroom practice implies that the structure of lessons making up teaching may differ and subject to change over time. The aims of this study were to investigate changes in observed lesson structure, and explore the effects of several teacher and contextual characteristics on differences in lesson structure during the first year of secondary education in Indonesia. Fifteen mathematics and English as Foreign Language teachers teaching 32 classes were videotaped four times (32 × 4) across the entire school year. A coding protocol to assess lesson structure focusing on the pedagogical functions of lessons was used. Six lesson components characterizing the general structure of the lessons were observed: introduction, review, introducing new content, student work time, closing and other. Multilevel growth curve modelling was used. Results revealed the six elements of lesson structure to be present, with student work time as the most frequent element. Relatively large class differences in lesson structure were visible. Evidence for changes over time in the components of lesson structure was evident as well. Teaching subject, class type and teaching experience explained differences in lesson structure. This study provides a global discussion about what matters in teaching from the perspective of lesson structure.