Hi Nic,
We’re a relatively young school at just 38 years old, and we’ve also combined our 10, 20, and 30-year reunions into a single event. Turnout varies quite a bit from year to year, depending on the cohort and how close they were at school. Generally, the 10-year group draws the largest crowd, with the 30-year cohort not far behind.
As Kimberley mentioned, having someone in the cohort who can rally others makes a significant difference to attendance. I try and find someone each year to encourage this but its tricky. I’m still weighing up whether this reunion format is the most effective way to connect alumni, but so far I haven’t found a better alternative through my research.