It’s autumn, the colorful leaves are falling in the outdoor classroom, and 2nd graders need practice with skip counting, flexible addition/subtraction strategies, and using models to show their work. I had noticed that the concept of 100 was not yet solid. Students were using millions and thousands to describe much smaller amounts. To address their math needs, along with their desire to be in nature, we visited our outdoor classroom to gather 100 leaves in three minutes. The students were paired and had drawn out their strategy before going outside. Counting one by one was NOT an option. Their strategies included:
stacking leaves in piles of 10
each child counting out 50 leaves by skip counting
counting out the first 10 and estimating the other nine 10s
After the first trial, the results were: 8, 18, 25, 51, and 140. A class reflection followed to generate new and improved ideas. As it turns out many pairs had resorted to counting one by one.
The second time, the students were more efficient and used estimation and skip counting to get closer to 100. One pair conducted a divide-and-conquer approach. They made a group of 10 together by finding two groups of five leaves. Once they had 10, they duplicated that by making a pile that appeared to be the same height.
The results were much closer the 2nd time:
82, 91, 94, 97, 100* (* there may have been some leaves added at the end, but they were certainly close to 100).
Laura Waite, Otisfield Community School, Grade 2