Same rigour. Different purpose
The purpose of an assessment centre is to choose between candidates.
The purpose of a development centre is to more fully understand the capability and behaviour of the people you already employ. The exercises and approach look very similar from the outside, but with a different focus.
There is no appointment or rejection decision at the end. All participants are engaged on the basis that they know the day is about helping and supporting them. That usually means they may behave more openly and honestly from the outset, providing clearer and richer evidence to work on. Feedback is not an enhanced courtesy service, it’s the core purpose of the entire exercise. The output is a detailed and enhanced development plan, not a hiring recommendation.
In simple terms:
If you are recruiting people, you want to look at an assessment centre.
If you are investing in employees, you want to look at a development centre.
And don’t try to do both at the same time - they are different.