How do these two options stack up to just not using Rails and using something like Sinatra instead for beginners? When I started with Rails, I spent 2 days figuring out the standard web framework functions / workflow, and then I gave up. When I picked up Sinatra, the pieces were small enough that I could learn them individually, master them, and learn how they were put together. Then, when I came back to Rails, I had…
With Sinatra you have absolutely no guidance as to what's good and what's not: there's no stack at all. I, too, am a bottom-up learner, but most people (in my professional experience) are not. Look at the success of Rails Girls, for example: beginners get waaay more excited and engaged by Getting Something Up There than they do learning the intricate details of HTTP.
This is much to the harm of components that might be a better fit for a project: I still believe that Sequel is a much better ORM for people that care about their SQL database and I frankly find it underused in the Rails world. Outside of Rails, its actually rather common, because it has a lot of merits.
I found teaching Padrino strictly better than teaching Rails (I do both), because you can teach it component by component and the missing "standard" stack is one of the reasons. Its much easier to teach it "the hard way".
[1]: Obvious, shameless plug: http://padrinorb.com , now with more development speed.