This study aims to explore the relationship between the occurrence of reflection (and non-reflection) and thinking activities (e.g., orientating, selecting, analysing) during portfolio-based conversations. Analysis of 21 transcripts of portfolio-based conversations revealed that 20% of the segments were made up of reflection (content reflection (6%), process reflection (10%), and premise reflection (4%)). The thinking activities comparing, analysing and concluding occurred significantly more often during reflection than during non-reflection. Orientating on the task, selecting and describing, occurred significantly less often during reflection. The outcomes show that the occurrence of certain thinking activities can be an indication of reflection.