Hang on, they applied for the same job that you got ... and yet are "not comfortable" about teaching the subject you both teach at "said level" - is it that you are expecting them to teach at the highest level, or are you suggesting that they teach younger or less able pupils? It's not quite clear from re-reading this which it is. That could have a bearing on their reaction. As a new broom, consider this: someone who has worked within a department and not got the promotion may well genuinely feel that they are not wanted, and can give nothing worthwhile, and be reluctant to move from their comfort zone. Presumably they have experience, and skills, and genuinely thought they might get the job. Did anyone from the Senior Staff debrief them properly after they didn't get the job? Has it been a taboo subject when you speak with that member of staff? It may be too late now, but perhaps the failure is still festering. Do you feel that you - and / or Senior Staff can drag it out into the open?