I know there's a lot of vague advice floating around about the Bain written case. Let me be specific about what I experienced.
You get a packet. Mine was 14 pages: a letter from a fictional CEO, revenue and margin data by segment, some market share charts, and a short exhibit showing customer survey results. The prompt asked me to diagnose why profit margins had compressed and recommend the two highest-priority actions.
30 minutes to read and prepare. Then a 10-minute presentation to two partners (no slides, you're just talking through your structure and recommendation), followed by 10-15 minutes of pretty tough Q&A.
The thing most people miss: they are absolutely not looking for a complete 80-slide BCG deck in your head. They want to see you identify the 2-3 most important issues from a noisy packet, commit to a recommendation, and defend it under pressure. I changed one part of my recommendation during Q&A when a partner showed me a chart I had underweighted. I think that helped rather than hurt me.
Timing is brutal. I did not finish reading the full packet before my 30 minutes ended. You have to triage. Read the prompt, skim the appendix exhibits, then build your structure. Don't try to absorb everything.
Feel free to ask specifics. Happy to share more.