I went through my first Train-the-Trainer program in 2000, when I was employed by ExecuTrain. At that time, it was a franchised computer learning center, much like New Horizons Computer Learning Centers. Every new hire for ExecuTrain, regardless of location, was required to attend a one-week Train-the-Trainer at corporate HQ in Atlanta. We were taught by senior corporate trainers. We covered everything from preparing for class, setting up the classroom, greeting students & introductions, setting expectations, pacing and tempo, effective presentations, demonstrations, engaging students, dealing with unexpected issues, reinforcing lessons, and adult learning theory. We were graded on two separate presentations by three senior corporate trainers. The program was pass/fail. If you passed, you returned to your training center, ready to teach. If you failed, your employment was terminated. It was the most comprehensive TTT I have ever experienced, including the CTT+.
Today, I wouldn't even know where to begin to advise potential new trainers on how to find a good TTT. Toastmasters, maybe?