>I spent up to 16 hours per week on one-on-one training in the first 6 months This is crazy. If the junior needs more than 1 hour a day to be net positive (= d

>I spent up to 16 hours per week on one-on-one training in the first 6 months This is crazy. If the junior needs more than 1 hour a day to be net positive (= do more work in the remaining 7 hours that you would do in that lost hour) then I would say they are a lost cause. This is also so easy to filter at the interview level - give them homework to learn some new skill, junior candidates are generally willing to spend significant time on that and it gives you much better picture of their abilities than whiteboard puzzle.