A headhunter contacted me in early March about PRTM. Even though I have seen them advertise a ton on job boards, I decided to work with the headhunter to get my resume in front of the "right" person. A few weeks later, after some email correspondence with HR, I had a phone interview with a Director (Partner). The interview was pretty basic (i.e. walk me through your resume, why PRTM, why did you leave so and so job, etc.). Most of the time was spent with me asking him questions about the firm.
After this initial conversation, it took about 5 weeks to be moved forward to the next round, which consisted of two face-to-face interviews in the office with one Associate and one Principal. I was surprised to learn of how case heavy the interviews were as there was little to no talk about my experience. About 15 minutes of the allotted 30 minutes was spent on a "case" while I was allowed to ask questions for the rest of the time.
A few days later I received word that the following week I would have another phone interview with a Director. This interview lasted about an hour with a mix of background questions (walk me through your resume, what are you looking to do in your next position, why PRTM, etc.) and a 15 minute case. A few days later I hear back from the headhunter. Basically, the firm wanted my 100% commitment to them BEFORE they would give me an offer. I was in the pipeline at a few different places and could not, in good faith, tell them that I was fully committed to them offer unseen. A few days later HR called to let me know that I was no longer being considered for the position because my "background did not fit their current needs".
Things to consider:
1) PRTM has a notoriously slow interview process with multiple (sometimes unnecessary) layers, so be prepared to be in the pipeline for months before really getting anywhere. If I had progressed past the 2nd phone interview, I would have had another round of multiple in-person interviews with Directors
2) The interviews are a lot more case-like than the firm and other people may lead you to believe. Have a pencil and paper ready and be prepared to discuss a business issue in detail
3) The firm seems to want "yes people"...people who are 100% committed to accepting their offer before they even offer. That says a lot about their culture
4) Just some food for thought: not sure how difficult this would be, but before working with a headhunter try to figure out what the relationship is between them and the firm you are interviewing with. I found that working with a headhunter who has a personal relationship with the hiring party makes the process a little more difficult since they may be holding back as far as really recommending you for the job if you do not show 100% commitment since they don't want to damage that relationship
