With the development of educational robotics, teachers of secondary and high school frequently request clear indications on which type of robot is most effective for strengthening students' mental schemes on the robot. This paper investigates whether using crafts and recycled materials or structured materials to build robots is more effective in terms of pupils' cognition in educational robotics. Some scholarship argues that using crafts and recycled materials to build a robot from scratch is more effective than using structured materials. The design of the educational research applied here, and in which we tested this hypothesis, included two different robotics activities, carried out in Italy with two classes of secondary school. In the first, we asked the students to build a robot from scratch using crafts and recycled materials, while in the other we asked the students to build a robot from structured materials. These two activities were preceded and followed by the completion, by students, of the same questionnaire about knowledge of mechanics, manual skills, conceptualization of robots, and beliefs about the robotization of everyday life machines, which were the learning outcomes identified in this study according to the concept of constructive alignment and outcome-based education. Results show that building a robot from scratch increases pupils' knowledge and manual skills, while building a robot with structured materials increases their awareness of the robotization of machines. Thus, current scholarship's approach is only partially confirmed. To conclude, although pupils' appreciation involves equally both these robotics activities, each of these outlines a specific educational outcome. [ABSTRACT FROM AUTHOR]