It stands to reason that the longer you work with a participant, the more impact you can have. This is mostly true, and I'm not going to bore you with a lecture on the law of diminishing returns.
This is all well and good but sometimes you don't know how long a particular person will be working with you. Maybe you have lots of different projects happening; some quite social and some more focussed. Just because June comes to Bingo on a Monday morning, which gets her out and about and socialising and has made a huge difference to her depression by the way, does absolutely not mean that she won't end up joining the fall prevention project you are running, and then becoming one of your community ambassadors.
Each individual who your charity or organisation works with, is exactly that, an individual - and each evaluation needs to anticipate the needs of that individual.
KRP Consultancy anticipates answers when designing evaluation frameworks, not to push people into giving certain answers (we are honest, and proudly so). Evaluation materials with KRP Consultancy are generally flexible and can adapt to the changes in participants lives, or the project changing. For that reason KRP often colour codes the participants. Every person fills in the same simple evaluation form, or answers the same questions online, or puts the same stickers on a board - whatever tools KRP has designed for your project.
The answers will all be the same to participants, but they may answer a yellow survey, or a green one, or a purple. They won't always notice (they'll often not notice at all) but all of a sudden, the answers can be analysed differently to represent different averages, different levels of intensity and a whole new set of useful answers can be shown.
Colour co-ordination can be an easy way to describe impact too. Yellow people are more confident than green, but purple have made the most changes in their health, or journey back to work, or happiness, or understanding. Then you can look at why purple have done better, and all of a sudden, the project has an area of focus. Something to build on and something to shout about.