Spatial skills are fundamental not only for engineers and architects but also for professionals in a great variety of fields. These skills are crucial also in the academic training of students of all ages. In the academic year 2012-2013, a large-scale study was made at the University of Granada (Spain) to evaluate the influence exerted on these skills by several factors related to personal aspects, experience, hobbies, and abilities. At the beginning of the term, a spatial test and a questionnaire were administered to 750 students in three majors (Bachelor's degrees in Civil Engineering, Chemical Engineering, and Industrial Electronic Engineering) who were studying courses on Graphic Expression. During the semester, the students were invited to participate in a set of voluntary spatial skills training activities based on exercises of freehand sketching. At the end of the term they were administered a spatial test again. General intelligence, problem-solving ability, gender, construction games, and experience in technical drawing are the factors more directly related to spatial skills. Furthermore, the training activities have shown a high degree of effectiveness in improving the students' spatial skills.