New for 2018 is Keys to Transposition: A Method for the Teaching & Learning of Transposition on the Horn by Pete Nowlen with Brian O’Donnell and Heidi Oros.
One of the key tasks for a horn teacher is to guide their students toward learning and improving skills they need to be successful horn players. And no matter what level you achieve as a horn player, if you play in orchestras at all you will need to transpose.
There are ways that horn teachers tend to work on transposition; most often it is some combination of Kopprasch in keys other than F and study of orchestral excerpts. In my own teaching this is most typically the case, but I did include a series of short studies for transposition in my technique book (now out of print), Ultimate Horn Technique.
What the authors have done is develop essentially a hybrid publication that presents a method to learn transposition. The publication contains not only excerpts such as you would see in an excerpt book but also short studies and text written to guide the student successfully toward mastering the skill of transposition.
I believe a lot of teachers have developed their own tactics to teach the skill, but still this is a publication that should be explored by teachers working with advancing students, especially those looking for a comprehensive method of teaching transposition that is all laid out in print.
Published by Ensemble Publications, this 88 page book is nicely printed and bound. Adding appeal are a number of photos of historic horns and references to further sources, which include a number of references to articles in Horn Matters. Reasonably priced at $24.95, sample pages may be found here.