Iterative Design
One of the amazing things about 3D printing and digital fabrication is that it empowers users with the ability to engage in rapid iterative design.
Many projects lend themselves to only a single iteration; a bookshelf, or a raspberry pi radio transmitter, or a bamboo bicycle frame. Once the project is complete there isn’t a reason, or room or resources for another iteration. Classrooms are the same way with time usually being the limiting factor. The need to cover content gives students a single chance to demonstrate knowledge in a very narrow way. Even project features designed to gives students a chance to iterate don’t usually work for that purpose. A rough draft isn’t a working version but just a check in point for the half-finished project. Students need a chance to complete something and then iterate on that experience. Refining the product. Refining their learning. Learning to adapt.
Small projects can be powerful teachers.
A personal example is the Daddy Dollar. My children’s school gives out Dolphin Dollars when students are ‘caught’ being good by staff. I wanted to echo that positive reinforcement at home by creating Daddy Dollars.
-The first Daddy Dollar was created in Tinkercad as a beveled disc with a dollar sign printed in clear PLA. The model worked as a token.
-The second iteration used a Sharpie to highlight the dollar sign so that the symbol would pop.
-The third iteration tried an opaque filament instead of transparent.
-The fourth iteration out of a grey filament echoes a metal coin.
-The fifth iteration has the symbol punched through the disc so that it can be seen on either side as well as being strung together on a string. The new version prints more quickly and uses less material.
-The sixth iteration uses a darker colored filament.
-The seventh iteration returns to the grey filament to more closely resemble filament.
-The eighth iteration uses BronzeFill from ColorFabb to closely emulate a metal coin. 
Each iteration allowed for experimentation with design, color, post-processing technique and materials. While the difference between individual iterations is small the leap from first to last iteration is huge. Digital fabrication tools such as 3D printers, laser cutters and vinyl cutters lend themselves to this sort of rapid iteration.
Imagine if every project or skill a student attempted ended at that first attempt.
Small projects are powerful teachers because students can try/fail/succeed/refine before they say for themselves that they are done.
Give iterative design a chance in your classroom.
Daddy Dollar design is available on Thingiverse at http://www.thingiverse.com/thing:1013953/
Have your own iterative design story or resource? Please leave a comment or contact me on Twitter @DesignMakeTeach or on Facebook at Facebook.com/DesignMakeTeach. I love to talk with teachers, designers and makers about 3D printing and Learning by Making.