In a similar activity, we estimated how many jewels it would take to fill the smallest beaker. After counting and finding the actual numbers, we poured the jewels into larger containers. Again, in the tall, narrow cylinder, the jewels almost reached the top, while in the much wider beaker, they barely covered the bottom. Although the taller cylinder appeared to be fuller, both beakers contained the same number of jewels!
Understanding the idea of conservation of number, length, mass, liquid, and capacity require logical thinking skills that develop gradually over time. Although it is tempting to focus on only one detail such as the length of the row of cubes, the position of the rulers, the shape of the piece of playdough, or the level the water or jewels reach in a cylinder, our students now also consider other important facts when assessing quantity, mass, and capacity. We believe that children progress through specific stages of development at their own pace, and it is very exciting to notice how this aspect of their cognitive reasoning has grown in recent months.