There are so many uses for plastic containers! Here we've made subtraction machines made of SEE THROUGH plastic containers. (mostly from the deli, although one is a President's Feta container and some others are condiment containers)
They're super simple to make. Make sure each container has a removable lid. Choose your counter objects (anything from dried beans, the same sized buttons, marbles, fuzzy little craft pom-poms, etc. )The key is that these should be 3-dimensional and all the same size. i used little ¾ inch wooden cubes for the larger subtraction machine and very small wooden discs for the subtraction machine made from a condiment container. Cut a hole along the side of the lid that is JUST big enough (not too big) to let a counter pass through, one at a time.
How to use these:
Give each user a recording sheet (see below)
The student drops a number of counters into the container, counting while being done. The student writes the number of counters that were put into the container. The number is written on the first line in the column "Put in". The student closes the container with the cover. To be sure that the "shaking out" process doesn't take too long, choose a long word for the student to say (once, twice, whatever amount of times you want) while shaking the container and trying to extract some counters. (student should hold the container upside down when doing this) I found that the word "supercalifragilisticexpealidocious" works great. The shaking stops when the spoken word(s) ends. The student then counts the number of counters that have fallen out and writes that number on the first line in the column "Fell out". Last, the student looks into the subtraction machine (through its clear sides) , counts the remaining counters, and writes that on the first line in the last column.
Refill with a different number of counters or keep the same counters but do a different number of "fall-outs" as many times as possible. Write the results on the recording sheet, starting next to a new happy face (new line) each time a different "subtraction example" is tried.