I wrote about how to run Sprint Planning 1. We tried the same approach a few weeks ago with more than 100 people in one room (more than 10 teams working on the same product). We did a huge scaled Sprint Planning session 1 and 2. Believe it or not … it worked. People were very happy and most were not only surprised but also became convinced that they will do a good job.
The secret behind this success was to rely on the process that I described and by adding synchronization Scrum-of-Scrums every 30 min. The first SoS was messy but the last one ( #6 or #7) was incredibly productive.
We started on time at 09:00 and we stopped the planning at 17:30 on time. Timeboxing rules!