I begin by showing my students this launch video. This really helps to build excitement regarding the lesson.
I make sure everyone understands the expectations by asking what materials they need to use, what they need to do with the materials, and where the problem should be. I also make sure they understand the three different ways that they can demonstrate their solution.
I give them a few minutes to roam around the classroom and look for problems they could address with magnets. They also use the time to discuss their ideas with peers.
Next I have them create a three column chart labeled Ideas, Benefits, Issues. I demonstrate filling the chart by explaining an idea that would open the classroom door remotely, how it would help us, and then what design issues would come up.
I don't let them develop an idea until they have at least 3 in their chart, focusing on the process rather than product. Once they have an idea, I ask them to commit to how they will represent their idea to the class, through video, a written paragraph and diagram, or a rehearsed presentation.
When they are actually ready to create their designs, I had enough disc magnets (30 or so for a dollar at the dollar store) for each student, but if they were just creating a drawing or creating a mock-up like the one in the video, they didn't really need the equipment.
After a few days, they demonstrate their solutions. The students that drew pictures place them on their desks for a gallery walk, any students that chose to present their ideas do so, and we show videos from students that chose to record their explanations.