The Girls Friendly Society (history of the GFS) was set up in 1875 to help single women working in the cities, particularly in factory situations. Sponsoring companies collaborated with the society to offer a start in life in these new environments (in the 19th century, nearly all young single women went into service or just helped at home. In 1916, the certificate below was awarded to Miss Agnes Smart on completion of 3 years work at Baxters Bolt, Screw and Rivet Works (as she was getting married the next week, she could no longer be a member of the GFS; only single women could be members).
There is a picture of Agnes Smart in uniform (age 16-20 in all probability, i.e. 1910 to 1914) with six other young women. As she was working class, it is unlikely this was a private school. But it may have been a photograph taken at a GFS study class.