1977, John Le Carré, The Honourable Schoolboy, Folio Society 2010, p. 239:
This was the first leg of his labours. The second began with […] the names of such Shanghainese officials who, in consequence of criminal pro-Russian leanings, had been officially purged, humiliated or sent to a May 7th school to rediscover the virtues of peasant labour.
Etymology
Named after Mao Zedong's directive of 7th May 1966 calling upon all people to study industry, agriculture and military affairs.