Due to high linguistic diversity, the legacy of colonialism and the need for knowledge of international languages such as English and French in employment and higher education, most schooling in Africa takes places in languages that teachers and pupils do not speak natively, and in some cases simply do not understand. There is considerable evidence that pupils schooled in a second language achieve poorer results than those schooled in their mother tongue, as lack of proficiency in the second language impairs understanding and encourages ineffective rote learning.[17][18] Although UNESCO have recommended since the 1950s that children be taught early literacy in their mother tongue, progressing later to other languages, not all African countries implement this effectively.