Practical work in school science plays many essential roles that have been discussed in the literature. However, less attention has been paid to how teachers learn the different roles of practical work and to the kind of challenges they face in their learning during laboratory courses designed for teachers. In the present study we applied the principles of grounded theory to frame a set of factors that seem to set major challenges concerning both successful work in the school physics laboratory and also in the preparation of lessons that exploit practical work. The subject groups of the study were preservice and inservice physics teachers who participated in a school laboratory course. Our results derived from a detailed analysis of tutoring discussions between the instructor and the participants in the course, which revealed that the challenges in practical or laboratory work consisted of the limitations of the laboratory facilities, an insufficient knowledge of physics, problems in understanding instructional approaches, and the general organization of practical work. Based on these findings, we present our recommendations on the preparation of preservice and inservice teachers for the more effective use of practical work in school science and in school physics.