Background: Constructing knowledge through collaborative practical work is a complex process and involves the use of multiple modalities by group members. In practical work sessions, students often manipulate visual objects or textual materials but do not develop their scientific ideas. Purpose: This study illustrates (a) the challenges that science students face when they create thematic patterns in a laboratory class and (b) characterises the processes of how students make meaning of practical work activities. Sample: Drawing from a video database, we chose to investigate an 80-min chemistry lesson with eight Year 10 students who were unpacking the complex ideas behind practical work. This lesson episode was transcribed multimodally, with snapshots of the pictures of students' actions and gestures. Methods: This study adopts a case-study approach. A multimodal discourse analysis approach was taken to examine the classroom discourse of the students when they were determining the strength of acids and alkalis through electroconductivity. Results: We identified various challenges when students integrated gestures, pictures and verbal discourse during the practical work section. These challenges include those when students realise textual and visual modes and those when students associate components of apparatus into a system of functional set-up. Moreover, students cannot construct thematic patterns because they reorient their focus from the domain of ideas to the domain of objects and observables. The study recorded a number of strategies that students use to overcome these challenges that impede their meaning-making. Conclusion: The findings of this study contribute to the literature by identifying the challenges and strategies faced by students when they were connecting the scientific ideas with the practical work. When science education researchers advocate an inquiry oriented approach, they should provide ample scaffolds for these multimodal challenges.