As many as 390,000 ethnic Chinese, two-thirds of those with rightful claims to Indonesian citizenship renounced their Chinese status when the treaty came into effect in 1962. On the other hand, an estimated 60,000 ethnic Chinese students left for the People's Republic of China in the 1950s and early 1960s. The first wave of students were almost entirely educated in Chinese-language schools, but were not able to find opportunities for tertiary education in Indonesia. Seeking quality scientific professions, they entered China with high hopes for their future and that of the mainland. Subsequent migrations occurred in 1960 as part of a repatriation program and in 1965–1966 following a series of anti-communist violence that also drew anger toward the ethnic Chinese. As many as 80 percent of the original students who entered the mainland eventually became refugees in Hong Kong. During China's Cultural Revolution (1966–1976), Red Guards questioned the loyalty of the returned overseas Chinese because of their foreign connections. They were attacked as "imperialists", "capitalists", "spies", "half-breeds", and "foreign devils".As most had grown up in an urban environment they were sent to the countryside, told to "rebel against their own class background", and eventually lost contact with their families.