Give em small projects and code review them big time (kindly of course). Accept a bit of argument (i.e. don't get hung up on requiring humility from the junior,

Give em small projects and code review them big time (kindly of course). Accept a bit of argument (i.e. don't get hung up on requiring humility from the junior, mistakes bring that on their own). Do not be time constrained on these initial projects but keep on top to prevent interminable bike-shedding or pursuits-for-perfection juniors often have. If no improvement is shown over time, there is just not much you can do...sometimes mentoring means recognizing when it's fruitless.