Students in the After School Program are regular users of the STEAM Lab. We often do Snap Circuits or play around with our set of 3Doodler pens, but sometimes students just want to mess around with materials. On days like this, we engage in a RMBC - Random Materials Building Challenge. This kind of activity promotes divergent and creative thinking, problem solving, and engagement - rarely do I have students off task when we're doing a challenge.
Each student (or team, if working with teams) starts with the same set of randomly selected materials gleaned from the recycle piles in the STEAM Lab. It could four drinking straws, a 5" length of twine, a small cardboard box, and a marble. Add some basic adhesive like tape, and go for it.
You can set a competition framework - provide an objective and award points based on achieving it, or creativity, etc - or a more open ended project (invent something!), and see what happens.
These are endlessly scalable, able to be differentiated for a variety of age groups, skill levels, objectives... You can allow students to trade materials with each other, or add in a "bonus ingredient" halfway through the allotted time... however you set it up, the big thing is to provide an open space for students to explore and create something neat.
With two 3D Printers (a Monoprice Maker Select Mini and a Flashforge Finder), SDMHS students are able to physically manifest some of their cool 3D designs. In Mr. George's Geometry class, students created complex polyhedron shapes to explore measurement of volumes and angles. Printing them off gives us an opportunity to examine why some 3D prints work well and some fail.
For example, a shape with parts that are thin or spindly can be too weak to survive removal from the print bed. Thicker 'arms' generally make for better prints.
Getting to see a design fail is instructive - it forces students to analyze what went wrong so they can improve it, requiring critical thinking and problem solving.
The other conversation we have about 3D printing is around responsibility and originality - we print with a purpose, and we don't plagiarize. Many students have downloaded already-created items off of sites like Thingiverse and 'remixing' them by altering the files in Tinkercad or similar programs. While this is a great learning experience, helping students understand how complicated designs are made, my rule is that I won't print things that students didn't design themselves. I also won't print just anything, for any reason. Given the amuont of waste plastic that 3D printing produces (both on the manufacturing end and on the user end) we're working to source recycled 3D printer filament, and we hope to purchase a filament recycler at some point. In the meanwhile, I'm asking students to hold off on printing that cool wannabe fidget spinner or spiky nametag - things that will be discarded shortly and end up in the waste stream.
What I will print is student-designed prototypes. One student has a plan to create custom Magic card carrying boxes. Before he invests money in purchasing a roll of filament of his own, we're printing a prototype for him so he can see his design in real life, make adjustments, and perfect the design before production. Before he moves on and his production run starts, we'll sit down to create a business plan, complete with costs and timelines, so he can really understand what the project will mean. 
Students in the After School Program are regular users of the STEAM Lab. We often do Snap Circuits or play around with our set of 3Doodler pens, but sometimes students just want to mess around with materials. On days like this, we engage in a RMBC - Random Materials Building Challenge. This kind of activity promotes divergent and creative thinking, problem solving, and engagement - rarely do I have students off task when we're doing a challenge.
Each student (or team, if working with teams) starts with the same set of randomly selected materials gleaned from the recycle piles in the STEAM Lab. It could four drinking straws, a 5" length of twine, a small cardboard box, and a marble. Add some basic adhesive like tape, and go for it. 
