My second grade classes had previously been working on the concept of odd and even numbers during the past week. In order to review this concept and ascertain that the students had grasped the idea of odd and even numbers, we had a discussion about birth dates. To determine if their birth date was an even or odd number the question was asked, "Is your birthday an odd or and even number?" Most of the children used Brandon's strategy--even numbers always end with a 0, 2, 4, 6, or 8 in the one's place.

Harvey, whose birthday was celebrated on the day of the discussion, developed his concept with cupcakes. Harvey had three cupcakes and his mother had three cupcakes. Three plus three is a double, and doubles make even numbers.

Anthony used Brandon's strategy and knew his birthday was an even number because it ended with a zero in the one's place. Angel and Dan both used the strategy that doubles make even numbers for their answers. 2+2=4; xx+xx=4.

Miranda is one of a few children in the class whose birthday falls on an odd number day, November 13. She was stumped. She knew 13 could not be made with doubles and when she tried Brandon's strategy, that did not work either. She said her birth date was an odd number, but she could not explain the reason it was odd. Ryan's solution to her problem was, "If it isn't even, don't worry, it has to be odd." Although most of the birth dates in my class are on even numbered days, many of the children seem to grasp at least one strategy to determine if a number is odd or even.

Following our review of even and odd numbers, we moved on to some "Big Time Adding" on a partially filled in 100's number chart. We began with rote counting on the number line from zero to one hundred. We had discussed the concept of adding ten to any number, but had never examined the strategies for doing it. We started with the 10's column on the 100's chart. "What do you notice about this column?" Jeremy observed that a zero was in the one's place of every number in that column. He counted from 10 to 100 and said he added 10 to each number as he counted to 100.

I asked Richard to start with 40 and add 10. He said, "I jumped right down to 50 on the chart because I knew 50 was 10 more than 40." Anthony said, "I started counting at 41 and counted 10 more to make 50."

We moved to the 9's column. Kayla observed that all the numbers in the 1's place were 9's and the numbers in the 10's place go up by one 10.

Other addition examples were:

Lynell added 49+10.

Marion added 59+10.

Marcus added 69+10.

I asked someone to start with 20 and add 30. Jeremy said, "50, because 2+3=5 and you just add a zero to the 1's column." I asked someone to start at 50 and add 40. Miranda answered, "90, I started at 50 and went down 4 spaces. That's as far as I could go."

We continued by using some subtraction examples instead of addition. I was pleased to see that most of the children understood the concept of numbers increasing by 10 when they add 10 and decreasing by 10 when they subtract 10. Brandon discovered there were ten numbers between any given number on the chart and the number below it. That made adding more than ten or less than ten easier to do on the chart. We filled in all the missing numbers on the 100's chart by finding numbers before and after the numbers that were previously filled in on the chart. We colored in the even numbers to 20 on the chart. Miranda observed, "We're counting by 2's." Angel said, "We are skipping every other row." Marion said, "All the numbers we colored are even."

The use of the 100's chart helped the children develop concepts of numbers that come before and numbers that come after a given number. We developed strategies for adding 10's and subtracting 10's from given numbers. We observed the patterns of even and odd counting by using various numbers on the chart. Brandon's comment was, "This makes math more fun and less work!"