*2.1. Sample*

The sample consists of 583 Primary School (PS) students (307 boys and 276 girls), belonging to fourth, fifth and sixth grade of nine public centers. A total of 27 different classrooms in Lugo and A Coruña. The sample selection corresponds to a simple random sampling. Table 1 shows the distribution of attendants by course, center, and region.

The procedure to collect the information consisted of communicating with the centers obtained from the random selection process, of which four rejected the study proposal. The first contact was with the directors of the schools and later with the tutors of the course. The research was explained to the teaching staff, as well as the guidelines for solving the questionnaires.

Figure 1 shows the sample distribution by school and course. The fifth course of School 5 and the fourth course of School 6 stand out for a greater number of students, which is because they were centers with two small lines in both courses. Their classroom conditions were similar from a technical point of view (number and surface area of windows, orientation, sunshine, classroom size), so they have been presented together.


**Table 1.** Sample distribution by course, center, and region.

**Figure 1.** Student distribution by schools and courses.
