Internal migration mainly affects many rapidly urbanizing middle income countries, such as China, where more than one in three rural children are left behind by migrating parents. International migration mainly affects high income countries, where immigrants make up at least 15% of the student population in half of schools. It also affects sending countries, More than one in four witness at least one-fifth of their skilled nationals emigrating. Displacement mainly affects low income countries, which host 10% of the global population but 20% of the global refugee population, often in their most educationally deprived areas.