I found the rainbows on Pinterest, but the link didn't lead me to any directions. Here's how I made them. Each child got 12" strips of paper in each color of the rainbow. We then measured and cut them to match these numbers.
Talk about lots of practice measuring! I also got to talk about the idea of ROY G BIV, which helped each child put their strips in the right order. After they got their strips ordered and the ends all lined up, I came around stapled the lined up end for them. That left the other ends nowhere near lined up, but there's always one in the crowd who can figure out how to pull them all together and line them up anyway. Once I got that person's second set of ends stapled, they became available to help those who just didn't get it. In the end, they are colorful representations of how much these kids have learned about measurement!
If you're wondering what the writing on the strips is all about, we labeled each one.
r = 12 in.
o = 11 in.
and so on