* Robert Raikes (1780s): Raikes, a Gloucester printer, is often credited with popularizing the concept. He began teaching poor children in Gloucester, England, to read the Bible on Sundays, aiming to keep them off the streets and provide moral instruction. This is often cited as a significant starting point, but it wasn't a completely novel idea.
* Earlier precursors: Similar initiatives existed before Raikes, with various individuals and groups offering religious instruction to children, particularly those from disadvantaged backgrounds.
Therefore, there's no single "invention" date, but the 1780s, with Raikes' efforts, are generally considered a crucial period in the development of Sunday school as a widespread practice. It then spread rapidly throughout Britain and beyond.