I was talking about AD&D2 and D&D3 materials. It's my understanding that AD&D2 and D&D3 are considered of the "New School" by those who separate things by "Old" and "New" schools.
Speaking as a self-declared "old skooler", I would say that it's a little more complex than that.
Largely, 1e was old skool. Most 1e modules that I am familiar with certainly are. There are exceptions.
Largely, 2e was new skool. I'm not very familiar with many 2e modules, but a goodly number of the adventures I have seen were definitely new skool in my book. Again, there are exceptions.
3e split the difference- a good amount of 3e stuff is old skool, a good amount is new skool.
Rather than relying on the era its from, where a given adventure comes down in the divide often comes from its attitude and presentation.
Old Skool Adventure Examples (to me, anyway):
Tomb of Horrors
Keep on the Borderlands
Secret of Bone Hill
EGG's Greyhawk
Savage Tide Adventure Path [kudos for having "if the pcs decided to be bad guys" info throughout]
Gates of Firestorm Peak
Expedition to the Barrier Peaks
Thunderspire Labyrinth
Red Hand of Doom
Demon Queen's Enclave
New Skool Adventure Examples (again, to me):
The OG Dragonlance modules
The Avatar modules
Almost anything Spelljammer
Keep on the Shadowfell
Pyramid of Shadows
Of Sound Mind
Now, note that while most of the "new skool" examples I give are not that hot (imho), one of them-
Of Sound Mind- is absolutely
fantastic. It has the flat-out most satisfying ending of any module I have ever run. (And it's written by Piratecat!) But it has a lot of what I consider to be "new skool" elements, most notably a heavy reliance on assumptions about the pcs' course of action. Interestingly, that reliance comes not through railroading but via prediction- which is a great technique if it works.
I guess the upshot of this is, Don't think that just because I consider myself "old skool" that I see "new skool" as
bad. It isn't bad; it's just that my preferences typically lie elsewhere. Certain "new skool" elements are great and I use them liberally (I'll pick templates as an easy example, though I don't really use 'em in 4e, I literally find it easier and more satisfying just to make a "half-demon carrion crawler" or whatever from scratch).
Also note that a lot of those are a mix, and while I put them in one category or another, they use a blend of both old and new skool elements. Some of the very best are that way- the aforementioned Of Sound Mind, Red Hand of Doom, Demon Queen's Enclave (another new skool adventure that I absolutely love), etc.