I do not wish to go into more details than what I said :)
I totally understand all the risk elimination processes you use (pre-evaluation, targeted selection, etc.) and I have no criticism towards that.
You (Sophie, Tom) both have a seemingly well working educational programme(s) (or at least seems so) reaching out to multiple educational facilities in your countries. Think about reaching out to "lower levels" (none of the Wikipedias are edited by "quality people only" as of now or ever).
(Btw I would be really interested in the "keeping ratio" - how many students became regular editors from the masses you've reached - 1/8? 2/37? 1/100? 3/2637?)
Balázs