This article presents an instructional strategy called Premise-Reasoning-Outcome (PRO) designed to support students in the construction of scientific explanations. Informed by the philosophy of science and linguistic studies of science, the PRO strategy involves identifying three components of a scientific explanation: (i) premise--an accepted principle or fact that provides the basis of the explanation, (ii) reasoning--logical consequences that follow from the premise, and (iii) outcome--the phenomenon to be explained. Based on a year of study in four physics and chemistry classrooms, the article reports on how the teachers integrated the PRO strategy in their science teaching.