In 1911, a group of Bahraini merchants demanded restrictions on the British influence in the country. The group's leaders were subsequently arrested and exiled to India. In 1923, the British introduced administrative reforms and replaced Sheikh Issa bin Ali with his son. Some clerical opponents and families such as al Dossari left or were exiled to Saudi Arabia and Iran. Three years later the British placed the country under the ''de facto'' rule of Charles Belgrave who operated as an adviser to the ruler until 1957. Belgrave brought a number of reforms such as establishment of the country's first modern school in 1919, the Persian Gulf's first girls' school in 1928 and the abolition of slavery in 1937. At the same time, the pearl diving industry developed at a rapid pace.