In this lesson, students use square tiles to build an array made up of columns of 2 and relate it to even numbers on a number path up to 20. As multiples of two are circled on the number path, students observe that the ones digits are 0, 2, 4, 6, and 8. Now, students are ready to name all other whole numbers as odd. They learn that odd numbers can be identified in contrast to even. Next, they learn that when 1 is added to or subtracted from any even number, the resulting number is odd. Finally, students apply all of the interpretations they have learned to discern whether or not numbers larger than 20 are even.