Good question.

We do know from Beedle the Bard that Care of Magical Creatures was taught before Marauder Era as was Herbology because Dumbledore's notes mention Kettleburn and Beery (Herbology teacher) and this is when Dumbledore is still the Transfiguration Professor. There was a DADA teacher in Voldemort's time too. I would imagine that the classes have stayed pretty much the same, although I wondered whether in the past Occlumency was taught.

Lupin certainly knows that Snape is a superb 'Occlumens' so maybe it was an option during their time at Hogwarts.