Complex sentence: National schools, established by the British Government with the Stanley Letter in 1831, were originally multi-denominational, with a six-member board of two Roman Catholics, two Church of Ireland, and two Presbyterians.
Split into simpler sentences: National schools, established by the British Government with the Stanley Letter in 1831, were originally multi-denominational. The schools were controlled by a State body, the National Board of Education, with a six-member board consisting of two Roman Catholics, two Church of Ireland, and two Presbyterians.