[TheThinkTank] How do you report "progress" to donors?

I am curious how people report some of the more qualitative gains (soft skills like critical thinking, decision making, delayed gratification, etc.) in students of earn a bike programs to donors in a way that indicates that their money is well spent. I am especially interested in ways that this is communicated to donors through means other than anecdotes. Whether it is right or not to find ways to quantify a qualitative gain, I am still interested in hearing strategies and success stories.