Sass’s Academy, later Cary’s Academy, was a London art school that provided training for pupils wishing to enter the Royal Academy. In No. 6 Charlotte Street, in London, Sass’s school would have the pleasre of teaching Charles West Cope and William Powell Firth, among others. The school was launched in 1813, and established at its Bloomsbury address in 1820 (http://www.victorianweb.org/art/institutions/sass.html).
Here is a 1910 excerpt on the school from The International Studio: