Afghan square for school class

[rebcam]

I'm so excited to begin teaching a knitting elective class! I will have about twenty 12-13 year olds in my class, and all but one is a brand new knitter. As a class project, I'd like to have them knit one square for an afghan. Okay, that's easy enough. But, I want them to knit a two-color square on the diagonal. They would begin with one stitch, increase each row until they have about 25 stitches, switch colors, and decrease each row until the bind off with one stitch. These squares, made of two different colored triangles, would be assembled together to make a really neat pattern. The squares would be in garter stitch only.

My question: what increases would you teach the kids? I tried casting on with one stitch and then knitting into the front and back of the stitch. This comes out fairly even, but that maneuver is going to be hard for some of the kids. I tried make one away, but that is leaving big gaps.

I'm not concerned (yet!) about the overall size of the square. I can adjust that later.

So, you experts...if you were going to write up the pattern for this, what would it look like?

Rebecca