This NYT Magazine article is a must read for educators, parents, and students (of any age.)
I would like to add that I believe 'character' to be at least partly--if only partly--trainable well into adult life. I know adults who have leveraged already-strong traits to improve weaker ones, and I've seen other adults who have let weaker character traits sap strength from their more developed ones. (rehab is full of people who've spiraled down in that way.)
And perhaps it's not necessarily obvious which positive character traits may save your bacon in adult life. In my case, what the researchers call "zest," may well be what's made late-blooming achievement possible, after I squandered assets of more than one kind throughout my twenties and thirties. "Zest," for me, is a kind of desperation to experience life as fully as I've intuited myself capable of doing, but have--or had--as of yet failed to do. Sheer desire for more has impelled me to fight against my own propensities to be distracted and irresolute, a fight I still wage.
When I was in grad school for philosophy (!), back in the 1980s, I wrote a (somewhat half baked) essay on desire as the quality most important in education. At the time, I was enamored of Israel Scheffler's essay, Of Human Potential. By "desire," though, I think I meant something along the lines of "character," as educable and trainable throughout one's life.
BTW: that essay got me invited to join a PhD in Education at Boston College, but I declined, partly out of not being able to make up my mind, partly out of not wanting to go into a field--education research--that I perceived as having less status. Sigh. That was probably one of the biggest missed opportunities of my life (though if you think me insufferable now, just imagine me with a Ph.D. after my name).