What's This?
Is it helpful to learn trigonometry with tau instead of pi?
This is an open educational question, and the only way to answer it is
for educators to try it with their students. This website offers some resources
for faculty who want to experiment with using tau to teach trigonometry.
[learn more]
Textbooks

College Trigonometry With Extensive Use of the Tau Transcendental
An open source trigonometry textbook.
[source code] 
Trigonometry With Tau as Circle Constant
Another open source trigonometry textbook.
[source code]
Learning Materials

Worksheet
Trigonometric functions of special angles.

Flash Cards
Trigonometric functions of special angles.
Experiences
What was the trigonometry learning and teaching experience like using tau?
This section is for
educators to share their experiences and insights.
Wish List
 Webbased flashcard sites like this one or this one with radians given in tau as well as pi.
 Circle constant tau allowed in WolframAlpha on par with the constant pi.
 Add circle constant tau key to graphing calculators such as the Texas Instruments (TI) 84+, the TI89, and the TINspire.
 Interactive websites and animations like this one available in fractions of tau as well as fractions of pi.