I agree with that as well, Polarbear-- but I really, really, REALLY dislike the point at which kind encouragement and an expectation of success turns into "you must just not be trying hard enough yet" and victim-blaming.

Some kids really can try their VERY hardest and only be barely passing students in algebra and geometry.

It's not that anyone is telling those students that they can't do math-- it's that they really are struggling to.

Schrödinger's cat walks into a bar. And doesn't.