None of the paid students dropped out. If you were paid the same amount to improve yourself and learn vs packaging boxes at an amazon warehouse, I think the decision is easy.

We didn't have an interview process (in terms of selection). I was originally volunteering at a local library at a Free Code Camp meetup and got our first couple of students from there (the ones who really needed help). Afterwards it was word of mouth.

Finding students wasn't hard. We ran a 3 month pilot at our local library to teach coding for free (our students teaching the public) and many students showed up. In Silicon Valley, libraries wants to provide more technical resource / training but there aren't enough volunteers.