I took theory at Peabody in high school, but it was of very limited value because I wasn't also taking composition. A bunch of scales and chords don't mean anything at all unless you put them in a musical context. In my senior year, we had enough interest, so one of the music teachers offered theory so we could get out of taking the art history class requirement, which would have necessitated us dropping music classes altogether. We spend the year doing SATB harmonization. It was a lot of fun and very valuable. All my real theory work has been trying to understand jazz and how to play it on guitar. Guitar is a great/horrible instrument to deal with, because you have to do so much omission/selection to play extended harmony with - let's just come out and say it - 3 and if you're lucky 4 strings. Probably the single most important thing you can get out of that is that you're doing all the hard stuff with the top 3 fingers, so your index finger can move around and hit a bass note, or sometimes the high note.