The Software Carpentry Foundation's board asked me for some stats on instructor training, and I thought other people would find them interesting as well:
In the year Nov 1, 2013 - Nov 1, 2014, our numbers were:
instructors: 360 helper: 163 learner: 3914
That gives us an 9:1 ratio of learners to instructors, but the reality is probably closer to 10:1, since we have all the instructors in our database but are still waiting for some recent workshops to report headcount. Note that "instructor" counts every time a person taught a workshop, including repeats, and similarly for "helper" and "learner". Note also that this significantly under-counts helpers, since they're often not reported or recorded.
Since September 2013, but not including the recent live round at TGAC and University of Washington, or the current online round:
started: 356 completed: 98 (27.5%) incomplete: 163 (45.7%) in progress: 95 (26.7%)
Note that half of those who drop out do so in the first four weeks. Note also that some people have been "in progress" for months, but even a few of those do eventually complete...
89 people who got their instructor badge after Sept 1, 2013 have taught for us, out of 126 who have been badged in that time. That's 70%, and the number will climb as the people who have been badged in the last three months (summer online training, TGAC, and U. Virginia) start teaching.
Of the people signed up for online instructor training in January 2015:
66 US 17 UK 15 Canada 12 Spain 12 Australia 5 unknown 3 Brazil 2 Netherlands, South Africa, Switzerland 1 Chile, China, Colombia, Germany, Ghana, Hungary, Ireland, Israel, Italy, Japana, New Zealand, Poland, Saudia Arabia, Singapore, Turkey
female 38 (25%) male 113 (75%)
That last statistic is better than the gender balance among our current instructors (20% female), but still much lower than where we were a year and a half ago (38% female).