I recently found out about François Gouin, a sort of proto-Charles Berlitz who wrote (in French) a book called The art of teaching and studying languages, published in 1880 and then translated and published in English in 1892.
I’ve only skimmed the book so far but it looks like it contains some real gems relating to the teaching of Greek.
Gouin was a classics professor who attempted to learn German initially using the grammar-translation method used for Latin and Greek. The beginning of the book recounts what an utter failure it was and it’s quite an amusing read with section headings such as “An attempt at conversation—Disgust and fatigue—Reading and translation, their worthlessness demonstrated”.
After observing three-year-olds playing with language, the light went off and he developed his Series Method, described in the bulk of the rest of the book.
He ends the book discussing implications of his findings for the teaching of Greek and Latin. Again, I haven’t read in detail but I did enjoy his scathing remarks about the uselessness of dictionaries for learning a language and his bafflement at the fact students can spend 12 years learning Latin at school and still know nowhere near what someone learning German for six months under his method would know.
If you’re interested in the history of second language teaching with particular reference to Latin and Greek, the book might be worth checking out. It’s available at Internet Archive.