Math curriculum ideas expand outward from their originators, like ripples in a pond.
In pre-Internet days, it was great to see teachers using photocopies of photocopies of photocopies of worksheets I created, such as "Make These Designs." Nowadays, of course, people can always download and print a fresh copy.
One day at an NCTM meeting, I was attending a talk by the wonderful Jo Boaler, along with perhaps a thousand other math teachers. Imagine my surprise when as an example of great teaching, she showed a video of students struggling with a Lab Gear perimeter problem. True, her point was about how the teacher managed the situation, but still, I was pretty thrilled that a problem I created (in a genre I created, even!) provided the opportunity for this teacher and her students to shine in front of this large audience. I later found out that Boaler's research concluded that the Lab Gear was a key ingredient in a successful high school math program.
Speaking of Lab Gear: a couple of years later, when visiting a middle school math class, I was quite pleased to see that the day's activity with algebra manipulatives was one of the ones I designed. After class, when talking to the teacher, I found out he had no idea I was the originator of the activity. He was doing it because it was in his textbook (the College Preparatory Math Algebra Connections.) As it turns out, the people who wrote that strand for CPM were long-time Lab Gear users, and were obviously inspired by my approach.
One more story: in the December/January issue of The Mathematics Teacher, the back page article (a department called "My Favorite Lesson") was about modeling exponential decay with ten-sided dice. This is not a super-original idea, but the details were so similar to an activity on my Web site that I was a little miffed. I contacted one of the authors, and found out that she knew nothing about me or my Web site. She had learned the activity from her now-deceased methods professor when she was in education school. Perhaps that professor, or someone she knew, attended a workshop I offered at an NCTM meeting, and the activity rippled out!
In each of these examples, my ideas reached more people —in some cases many more— than they would have if they had not been picked up by others. They were a foundation on which they built, adding their own ideas, a different presentation, or a more effective organization. Of course, it would be nice to be acknowledged when that happens. In the case of the ten-sided dice, the editor of The Mathematics Teacher agreed: an acknowledgment and a link to my version of the activity appears on the back page of the March issue.
Of course, this is a two-way street. I have learned many ideas from other teachers and curriculum developers, and built upon them. In fact, I have taken the unusual step of crediting the source of my ideas in the front of my books, in an attempt at professional courtesy towards those people who inspired me. It seems wrong that this is not standard practice in math education.
In any case, let the ideas ripple out!