Just had THE most fabulous time with my grade 10's. It was the introductory lesson on congruent triangles, but I didn't want to say the words "Congruent triangles" and give anything away.
So I gave them this geogebra worksheet, created by Evan Weinberg. They moved the segments around to form a triangle, then took a snapshot using their snipping tool. Then they went to this googledoc to insert their snapshot. I made it clear that under no circumstances were they to shrink or enlarge their image, I wanted the actual size. After we got just a few of them inserted, I moved my own triangle outline over theirs, sometimes flipping, sometimes rotating, and lo and behold, we all had the same triangle. So sss demonstrated without words, only by doing and comparing.
Next, they all logged onto their explorelearning accounts, and started the Proving Triangles Congruent gizmo. Did a quick demo of how to measure sides and angles, how to select the conditions, and how to play around with the triangles to see if they are definitely congruent, or not necessarily congruent under those conditions. Then they worked in pairs to fill in the slides of this powerpoint, using snapshots from the gizmo to back up their statements:
We'll see how it goes, but one way or another, it turned out SO much better than I thought it would. Maybe I'm not crazy after all!