I am a classically trained pianist with many years of teaching experience in the classical repertoire. I would like to expand my horizons and become more knowledgeable about jazz and pop piano music and be able to share this with my students. Where can I gain this knowledge?
The first thing you'll need to do is to understand jazz yourself. I'm sure you realize that. But what I mean is that I don't think it would be very useful to just have some recommended repertoire or a curriculum without first understanding it deeply enough yourself to be able make those decisions yourself.
Learning to play jazz yourself is a great way—and in my opinion the best way—to begin understanding the concepts you'd be teaching. But either way here are some things I'd work on understanding and/or playing before you dive in to teaching it:
- Listen to a lot of jazz and get it in your ear. Get used to the rhythm, the harmony, the melodies and the general form. For bonus points, take it further and analyze and transcribe some of the things that you really like.
- Learn some rudimentary history and some of the basics. Know the different styles. Know some song forms (rhythm changes, blues, modal, etc). Know the terminology (for example if somebody says "head" or "chorus").
- Learn the harmony. While much of it will be familiar to you and you'll have a huge head start, you'll need to know the idiomatic differences that make jazz jazz. This especially important for piano given that whether you're playing solo or with a band, the pianist is the one covering much of the harmony.
- Learn how to improvise (or at least how other people do). This a huge part of what jazz "is" and it's what people studying jazz end up putting most of their time into. It takes years to become an expert at this so don't worry about mastering it or anything. But I'd learn enough that you can get students started on it.
- Put this all together by learning tunes. Learn a lot of standards and listen to a lot of jazz and the other parts I mentioned should naturally come along with it.
One thing I think you'll find is that there's a little less agreement on the right way to do things in jazz which makes it tough to recommend any canonical resource or body of work to work through. Most people learn through a variety of resources and by listening to and copying from jazz that they like.
To learn jazz piano you need to learn to play by ear, by listening to things and trying to play them as they sound. Sheet music can be a useful crutch to help you while you learn this skill but it alone will not teach to play jazz piano, you'll just sound like a classical player "trying to play jazz".
I would recommend finding a jazz piano instructor to get you started, you'll probably find the experience of approaching the instrument from a new perspective very rewarding, and as a teacher yourself you know how the personal communication and knowledge of a good teacher is far superior to books alone.
With your skill and knowledge at playing classical piano, it will be hard for you not to apply that knowledge and training to the sheet music in front of you, and in many cases with jazz, that way of looking at things won't apply. In other words, the problem for you won't be what you don't know, it will be what you do know! Your natural response to jazz tunes will be to try to understand and interpret them through your existing musical framework, when you really need to approach them "as a novice", in order to not miss the wood for the trees so to speak.
Obviously your existing technical ability will make you stand you in good stead to learn how to play jazz, but when approaching jazz piano it is worth remembering that it is a completely new discipline, and so a teacher will be invaluable. I sometimes* find that classical players expect that playing jazz will come with minimal effort, since they already play very technically challenging classical works, and jazz is less "serious". Whereas in reality, I think a classical pianist would have more luck autodidactically learning classical flute or classical clarinet than jazz piano.
I absolutely LOVE teaching classical players to play jazz. It's incredibly rewarding. But my experience has consistently been that the first thing I have to do is ban sheet music from the room, because as soon as there are dots on a page "the training kicks in" as the military might say. Now, of course, I'm not at all saying that's the only way to teach classical folks to play jazz, (and I probably wouldn't take that approach for piano), but it illustrates how important the oral as opposed to the written side is for jazz instruction.
*I say sometimes, because in many cases the exact opposite is true, I've ran jazz & blues workshops with classical players who are sure they "can't play jazz" and were surprised at how quickly they found themselves playing it, once they were pointed in the right direction of how to go about it. In fact, teaching classical players to play a bit of jazz is one of my favourite things to do for this very reason.