Students work part-time, study in the evening, or take short intensive courses, leaving their workplaces for only a month or so. There are also "farm colleges", where rural workers can study to become engineers and assistant engineers, and a system of correspondence courses. For workers and peasants who are unable to receive regular school education, there are "laborers' schools" and "laborers' senior middle schools," although in the early 1990s these had become less important with the introduction of compulsory eleven-year education.