Here's some good reading:
And it does bring up the question: is attendance our main measurement for success? I work in event planning, so let's use that as an example. Are the most popular events the best ones?
In terms of what we report and measure, we certainly act as though popularity is the only thing that matters. But we know, we know in our hearts, that it's not. An event where 100 people watch a skateboarding dog is NOT a "better" event than a class where 20 kids use Lego to learn about science. I think most library people would feel like the science class was more valuable, and a better use of taxpayer dollars, than the skateboarding dog.
Which means that we need to use another framework to define our success. To put it another way, when someone asks, "How did the Lego program go?" we need an answer that doesn't relate to attendance. "It was wonderful, the kids had fun and learned a lot!" is a good start.
But of course, that's just a start. Most of the time, when we are explaining why something is valuable, it's important to be professional and convincing. Which means that you need to take that statement and turn it into something you can tell your boss, and maybe something you can tell the board, or tell the taxpayers.
My quick and dirty method for doing this is to find one thing to measure that isn't attendance.
Use your library's mission statement, your strategic plan, or your department's goals to figure out what this should be.
For example, if your mission has to do with learning, think about doing a quiz question at the end of the Lego class. Did the kids get it right? You can report that 90% of the kids in the class displayed an understanding of the such-and-such principle after your class. If your mission has to do with inspiration, try asking them instead if they plan to go home and use what they learned to make more Lego creations. If your mission has to do with providing opportunities, ask the parents whether they would have been able to do this with their child at home.
If you don't have a stated mission or goals, then just find some commonly-agreed-on Good Thing to support. If your boss is always happy to hear that people are checking out books, try setting up a display of Lego books in the classroom. Count how many of the items get checked out, or count how many kids take books from the display. Then you can say "75% of attendees checked out Lego books after the program!"
This is going to help you in several ways:
First of all, it will help you express the value of what you're doing. Right away, your projects will sound more purposeful and more impressive. If you work in a library (or other non-profit) then you probably believe pretty strongly in your work. This is going to help you get other people on board.
Second, it will actually add value to your projects. Here's a recent example from my job:
I was using this method to think about a "Hunger Games" party the library is hosting. I wanted something besides attendance to measure, and I wanted it to be related to reading. Maybe we could measure book checkouts somehow? Then I had the idea to create a cool read-alike book display that would encourage the teens to check out books. What a fun idea! And it doesn't just articulate the value - my program is better because of this idea. In a small way, I am better expressing our mission.
Third, it will help you prioritize. You'll be able to sit down and say, "What should I schedule for this summer? A Lego science class, or a skateboarding dog?" You won't have to guess which would be "better" - you'll have a framework that helps you evaluate which program fits with your organization and helps you accomplish your mission and goals.