Sunday school is a Christian educational institution for  children and young people.
I know it as Adult Bible study for the adults
I see. Seventh-Day Adventist and other sabbatarians hold their schools on Saturdays.
 Sunday Schools were first set up in the 1780s in England to provide education to working children
wrote an article in his journal, and as a result many clergymen supported schools, which aimed to teach the youngsters reading, writing, cyphering (doing arithmetic) and a knowledge of the Bible.
In 1785, 250,000 English children were attending Sunday school. There were 5,000 in Manchester alone. By 1835, the Society for the Establishment and Promotion of Sunday Schools had distributed 91,915 spelling books, 24,232 Testaments and 5,360 Bibles. The Sunday school movement was cross-denominational. Financed through subscription, large buildings were constructed that
School had 1,127 boys and 1,324 girls on its books when it opened. The building is now known as The Old Sunday School and is part of Macclesfield Museums.
Sunday schools were first set up in the 1780s to provide education to working children on their one-day off from the factory. It was proposed by Robert Raikes, editor of the "Gloucester Journal" in an article in his paper and supported by many clergymen. It aimed to teach the youngsters reading, writing and ciphering and a knowledge of the Bible