there's an episode of Downton Abbey where one of the servants said that he entertained notions of becoming a school teacher before his family made him leave school to get a job. Assuming he meant a primary school teacher how much additional schooling would that have required in around 1900?

by grapp
Capt_Blackadder

Well there were very few actual requirements to be a teacher in the UK. For example even 50 years beyond your time frame John Cleese managed to get a job teaching Science,Latin,English,History and Geography at a Prep School when he was 18 before going to University. So the answer is that at a minimum he would have needed to have his school leaving certificate and that would be about it.