To assess prior knowledge, provide each student with a blank index card and a resealable plastic bag filled with a set of cubes of two different colors. Ask students to create trains of ten and leave separated any cubes that might be less than or more than ten and to record the number of cubes in their bag on the card provided.
Have each student in turn read the number on his or her card and count the cubes found in the bag to verify the correspondence between the number reported and the cubes.
To begin the lesson, distribute a set of index cards to each student with the numerals 11 to 20 written on individual cards.
Place the students in pairs. Ask one student to show a card at random and the other student to model the number with cubes.
Give the students connecting cubes in two colors and a copy of the Ten Frames Activity Sheet.
Ten Frames Activity Sheet
Ask them to model 19 in the Ten Frames, counting aloud in unison as they do so.
Next, ask, "How can we change the ten frames to show 20?" Ask students to model other numbers to 20 using the numbers recorded on their index cards.
Now ask them to model the numbers 19 and 20 with the connecting cubes, 10 in one color and the remainder in another color.
Ask them to break the 20-tower into two parts (ex: 11 and 9). Call on a volunteer to describe how he or she divided the tower, and then record this on the board. Ask if anyone has broken the tower in another way and record these responses on the board. Repeat with several volunteers.
Now distribute bean sticks and beans. Give each student two bean sticks and a collection of at least 20 loose beans.
Ask students to look at a numeral card you are holding and model that number. Use cards from 11 to 20.
This will require that they "trade in" a bean stick for 10 loose beans. By trading loose beans for bean sticks with ten beans glued in place, students develop an understanding of the value of numbers in the 10s place by recognizing that 10 is a unit of beans rather than loose beans used to represent ones.
Count out the required number from the loose beans. This action will set the stage for later work with the addition and subtraction algorithms.
Ask the students to model and label bean sticks showing 19 and 20.
Reference
Burton, Grace M. Towards A Good Beginning: Teaching Early Childhood Mathematics. Menlo Park, CA: Addison-Wesley, 1985.