Their work consists in maintaining laboratories, preparing experiments, and assisting teachers in conducting laboratory classes. A total of 13 other professional categories are stipulated to support the day-to-day operation of schools (e.g. accountant, psychologist, nurse, librarian, clerk, secretary, repair man, guard, doorman) (See Annex 4.A1). The number of positions per category depends on the type, level of education and number of consolidated classes of the school. Norms for teachers, student-teacher ratios and “sanitary” conditions of schools mean that, within schools, most students are supposed to encounter comparable conditions.