My small PsyD program handles them really differently, so I'll be interested to hear what you guys think. I found it a really beneficial learning process, if somewhat artificial.
Our comps consist of three parts: clinical interview, report, and defense.
The clinical interview consists of us interviewing an actor for 50 minutes while videotaped. The goal of this will be to gather as much information as you can for an assessment while also using clinical skills and building rapport. Your video is reviewed by the comps committee, and they pick out a five minute segment to watch during your defense. You have to watch the video and explain why you approached things the way you did, and answer any questions the committee has about your process.
After the clinical interview, we are given 24 hours to decide which assessment measures we would want based on the information we have learned. We are allowed to choose up to 8 measures (out of a possible 10 - the tests are from a real client so they worked with what they had). We have to be able to defend why we chose each measure and why we excluded others. Once we submitted our choices, we were sent PDF's of the protocols. I was unfamiliar with many of the measures (ex: had not yet used to the WJIII), so had to learn about each of them, choose the ones I wanted, and then learn how to interpret the scores. It was a good amount of work.
We had ten days to write up a report that included history, assessment results, case conceptualization, and treatment plan. All of this had to fit into a 15-page (double spaced) document - this was not easy! You had to learn to be really concise and really highlight the most pertinent information. You were not allowed to talk about the case with anyone (partners, other psychologists, friends, people on web forums - no one).
After handing in our report we had a week to prepare for our defense. Then we had a one hour defense where we were grilled about the clinical interview, the assessment measures/how we interpreted them, our case conceptualization and our treatment plans.
They are tough and out of the six of us, only one got distinction and one had to rewrite. Last year two people had to rewrite and none got distinction.
So although it's really artificial, all of the information is taken from a real case, and I found it a really useful (if stressful) process that helped me feel more confident about assessment reports, case conceptualization, and writing concisely and under time pressure. Interested to hear all your thoughts, though!