After a few months they got the idea and I didn't have much trouble getting them to participate. Whether or not a student kept this up to date was up to them after a while. Once the behavior was established and as long as everyone participated or acted interested I was happy. I'd say less than 20% have this list in any reasonably updated form now.
Once May malaise set in I saw fewer making guesses. I wasn't mad, given how tough it is to keep anything going in a classroom for an entire year. The solution? Our Estimation Finale.
This would be our last interaction with Estimation 180, and we'd do a ton of days at once.
Take out a piece of paper, put your name on it, number it 1 - 15.
Choose a set of days to work with. I chose Day 159, 163, 166, 167, 169, 171, 172, 175, 176, 177, 178, 181, 182, 185, and 186. I displayed the questions and had them record an answer. Day 172 reveals the answer to Day 171, so that was a bit of an oops. All the other ones worked.
After we went through the 15 challenges I had them trade papers. I revealed the answers one by one. You get a check for being exactly right, a "C" for being close, and an "X" for being too far from the answer. The definition of close was different for each challenge, and we discussed what an acceptable range would be for each one.
In the end, we saw who had the most exactly right (5), close (13), and wrong (13). Each got a prize.
Fun way to spend 40 minutes. Very intense deliberations the whole time. I will probably use this with Pre-Cal during some down time we have ahead of us.