An estimated 20% of children leaving kindergarten fail to adjust to elementary school requirements and are in need of special schooling. Children with delayed development who "may" return to normal schools and study along with normal children are trained at "compensatory classes" within regular schools. The system is intended to prepare these children for normal school at the earliest possible age, closing (compensating) the gap between them and normal students. It is a relatively new development that began in the 1970s and gained national approval in the 1990s.