In high-school chemistry the pre-experimental phase of inquiry cycles often remains neglected. According to a procedural model, which is described in the text, this phase begins with an observation that stimulates students' prior factual knowledge, the formulation of a research question for further elaboration (epistemic questions), the anticipation of a hypothetical answer, and the planning of experimental steps for deciding on the hypothetical answer. These activities were explicitly prescribed in an experimental group of 28 10th-graders. Raising the quality of students' epistemic research questions by providing structured help was a special focus of the intervention. Hypothesised motivational and cognitive effects were measured and compared with a group of 25 students (control group) who engaged in non-structured pre-experimental activities. The intervention provided to the experimental group resulted in stronger preferences for a more open and non-recipe type of experimentation, in more intense cognitive activities (thoughts), and, most importantly, in increased skills for formulating causal epistemic questions. Supporting such procedural skills in classrooms may contribute to transforming labwork into intentional activities and students into active learners by helping them focus on further elaborating their knowledge. (Contains 3 figures and 5 tables.)