Latin grammar
I will say at once, quite firmly, that the best grounding for education is the Latin grammar. I say this, not because Latin is traditional and medieval, but simply because even a rudimentary knowledge of Latin cuts down the labour and pains of learning almost any other subject by at least fifty per cent. It is the key to the vocabulary and structure of all the Romance languages and to the structure of all the Teutonic languages, as well as to the technical vocabulary of all the sciences and to the literature of the entire Mediterranean civilisation, together with all its historical documents.
Dorothy Sayers, The Lost Tools of Learning (Paper read at a Vacation Course in Education Oxford, 1947)