Design and computer graphics curricula for tertiary education include 3-D modeling skills. Students have to learn to represent (complex) 3-D objects by means of parametric surfaces or polygonal meshes. Three-dimensional modeling may be a complex task and students have to be able to accrue a certain deal of experience in the field before passing the exam. The main difficulties the students have to face mainly concern the comprehension of 3-D shapes and the choice of the most appropriate modeling techniques. This paper proposes a framework to support bachelor students of the design degree in modeling 3-D objects by means of parametric surfaces. The proposed framework provides two augmented reality (AR) apps for smartphones and a web portal. The mobile AR apps allow students to deeply visualize 3-D object shapes, thus performing a set of guided exercises in order to take practice in basic modeling techniques. On the other hand, the web portal allows students to share their models with teachers and classmates to get feedback and comments. Preliminary results show the effectiveness of the proposed solution as all volunteers involved in the experimental phase achieved better results after using the tools. Moreover, the students' opinions about the proposed framework are positive.