The mathematics of team productivity

One of the best ways I have found to avoid the dividers is to give them a homework assignment at the end of their first on-site interview. A development project (like implementing a todo list with some special twist) and then coming back in and having some of the current developers peer review their code. The red flags to watch for:

1) reaction when given the homework assignment. Is there enthusiastic energy in their response or do they react with fear, uncertainty, doubt, or do they turn up their nose like the challenge is beneath them? If any but the first reaction, then dive in deeper with some targeted questions based on your observations. Sometimes they're still a good candidate but have been beaten down by prior work places, so you have to judge if their potential outweighs risk of a negative hire.

2) general disposition during code review: During 2nd onsite interview, they are there to meet and greet the larger development team and to defend their project challenge to a select few on the team. I let the developers welcome them and discuss the review process and help them settle in before going into the code review as this gives them a chance to relax and hopefully also realize "this is how its done here" -- In this session, one of two things generally happen. The candidate either shines and enjoys the whole review process and takes in the advice and critiques and willingly and quickly adapts to the feedback coming through, or he/she gets very defensive and closed-minded and shows little reception to what the team is saying.