Hold up a large clear container filled with small, countable objects. Ask your second graders to guess or make an estimation about how many items they think are inside the container.
Write down their answers on the board or ask them to remember their numbers.
Open the bag and together with the children count the number of objects to verify the accuracy of their estimations.
Repeat this exercise daily in order for the children to practice estimating the same number of objects by placing them in different types of containers or to see the ways that the same container can hold different numbers of objects.
Place two hula-hoops in the center of the classroom in the shape of a Venn diagram.
Pass around a bag full of red, green, and red and green balls or cards and have your second graders take a few balls and put them on their desks.
Show the children that the red balls go on one side of the hula-hoop while the green balls go on the other.
Call on the children one at a time or in groups to come to the front and put their balls inside the hula-hoops.
Ask them to decide on their own what to do with the colored balls, offering instruction or hints as needed. Ask the children if the hula-hoops have been filled in correctly and let them continue the analysis by checking their peers' work.
Prepare a bag or box of four times from four different categories. For instance, choose four kinds of fruits, four types of clothing, four examples of electronics, four types of tools for a total of 16 items.
Demonstrate to the children how to classify items by writing the names of the categories on the board and finding one example from the pile. For example, they could place a hammer as a type of tool.
Call on the second grade students to come forward individually or in groups to go through the things and classify them.
Pass out a worksheet with other classification activities so they can practice this data analysis technique.