Recent studies in science and engineering education support that inductive learning activities encouraging active student involvement may improve students’ motivation, development of soft skills and academic performance, compared to traditional lectures. Until recently, several technology-enhanced learning environments have been proposed to facilitate such activities in classrooms. However, these commonly depend on dedicated hardware devices, such as clickers or tablet PCs. Contrastingly, smartphones are being massively adopted by society as these become increasingly powerful and inexpensive. Even so, the use of smartphones as learning tools in lecture halls has still not been widely adopted. In this paper we present CollPhoto, a paper-plus-smartphone environment that supports face-to-face problem solving activities in the classroom. CollPhoto provides the instructor with instant visibility of students’ work, and facilitates him/her conducting discussions, based on a selection of students’ responses. We report on the design and initial validation of CollPhoto in the context of two computer science courses.