Conducting is, pedagogically speaking, a young art form. The first two real conducting “textbooks” were published in 1950. That year saw the publication of Max Rudolf’s The Grammar of Conducting and Nicolai Malko’s The Conductor and His Baton. Sure, others have written about conducting in the past, especially in the Romantic Era, when the need for conductors as we think of them today arose, but we don’t find much in the way of “how to” books about conducting prior to 1950.
Hideo Saito was a conducting pedagogue from Japan that developed a very particular philosophy about conducting and conducting technique. Essentially, the technique focuses on acceleration and deceleration to and from beats (I think of it as energy to and from a beat), but of course it’s more detailed than just that.
Here’s a video of Saito working in rehearsal (sorry there’s no translation of the Japanese):
Wayne Toews is the current leading teacher and acolyte of the Saito method. Here’s an interesting video of him demonstrating some of the basic technique:
One of the things I find most fascinating is how we are still finding our way about how to teach conducting! Forget even teaching how to study a score! (See maestro Mengelberg’s below:)