Remember Mad Libs from childhood? I thought I could piggy back off that idea for a math activity. I'm thinking either a part of the first day of school, or a day before a holiday, or some other such time. It wouldn't take all period. My guess is 15-20 minutes (longer if they do the "homework" in class). Here's a sample of one of two I want to make. I envision a "BAT" version and a "___" version with a different storyline on the back. Students should keep their version hidden from people with the other version.
Edited to note:
This idea is not affiliated with
MathLibs(R), a brand used in commerce for over a decade
(link to: http://kidcourses.com/mathlibs/ ).