their work consists in maintaining laboratories preparing experiments and assisting teachers in conducting laboratory classes a total of other professional categories are stipulated to support the daytoday operation of schools eg accountant psychologist nurse librarian clerk secretary repair man guard doorman see annex a the number of positions per category depends on the type level of education and number of consolidated classes of the school norms for teachers studentteacher ratios and sanitary conditions of schools mean that within schools most students are supposed to encounter comparable conditions