This Kindergarten lesson focuses primarily on K.OA.A.1 and K.OA.A.2. Students are solving addition and subtraction word problems using representations and by acting out situations in order to understand addition as putting together and subtraction as taking from. This lesson shows strong evidence for Core Actions 2 and 3.
Using Adding and Subtracting to Compare Numbers (Barnum)Download
Students can be overheard talking about their strategies to represent 7. One child can be heard talking about tally marks, while another student asks a peer at his group, "How you do take away?" It is assumed this child is clarifying his own mathematical understanding of subtraction to represent 7. This illustrates how math conversations might begin in such an early grade.
In this part of the lesson, the teacher randomly calls on two students to share how they represented 7. The first student shares a story problem ("I had 10 hearts, I gave 4 to my family.") that does not illustrate 7. The teacher has the student come up to the board to use the number line to count back 4 spaces from 10 at which point she realizes that she wants to change the number from 4 to 3. Next, the teacher calls on another student randomly and he shares a number sentence, 5+2=7. The teacher asks the rest of the students if they agree or disagree. Most agree. She then has the students show her 5 and 2 more. They count on (aloud) from 5 ("5, 6, 7").
Here, the teacher says she's thinking of a number less than 7. She calls on a student to share a number less than 7. The student says 2. She asks all students if they agree or disagree. Then she asks one student if he agrees that 2 is less than 7, and then, why? He tries to explain saying "7 and 2." The teacher says "What is 7 and 2?" She calls him up to the number line to show how 2 is less than 7. The teacher reminds students that as they go left on the number line the numbers are less and as she goes right on the number line the numbers become greater.
In this part of the lesson, the teacher uses students to act out a number story. She makes the math explicit by showing the students an example of a representation for 3-2=1 ("How many more boys are there than girls?"). The teacher calls on one student to share his thinking about how he knew the answer was "one more." He explains that they were the same for two boys and girls and then there was one more boy. The teacher repeats his idea so all students can hear it. She then has students turn and tell their neighbor how many more boys than girls there are.
In this part of the lesson, the teacher is checking for student understanding at one table group. She uses her fingers to represent the boys and the girls. She checks in with another table before asking the whole class again, "How many more boys were there than girls?" When the majority of the class shouts "3" she tells all students to draw a model of 2 girls and 3 boys. The teacher then adds to the story problem that each friend needs a reading buddy, a girl/boy reading buddy. She has students buddy-up the boys and the girls, and there is one boy without a reading buddy. In this way the teacher shows that there is 1 more boy than there are girls.
The teacher has given the students another problem to solve and she is checking for understanding. She is asking questions such as "Can you show me how you got that answer?" "How did you count?" "How did you do that?" "Show me how you did it." "How did you know it was 3 friends?"