In Rails Active Record is not a fundamental particle because we slip into SQL very often. Knowing this I would recommend that a person learning Rails actually start with enough SQL to pull off some select * from table statements from memory before attempting that first app.
What about jQuery on the front-end? Is the jQuery CSS selector such a good abstraction that I never need to manipulate the DOM without it? Is it worth my time as a novice to understand what jQuery is hiding from me? Is it enough that I get the gist or should I be able to implement a significant web app without it?