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Gr. K Unit 2 / Gr. 1 Unit 2~ Two Digit Numbers & Base Ten
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To younger students, single digit numbers are very much like two-digit numbers; they are used for counting objects. So, counting to 9 represents 9 objects, and counting to 16 represents 16 objects. As students learn the base ten system, they need to realize that numbers can be grouped in tens, the basis of our number system. It is also important to realize that a number like 25 can be represented many different ways.

Students use base ten blocks and digiblocks in class to represent numbers. This lesson completed with Kindergartners and first graders uses the base ten block virtual manipulative: http://nlvm.usu.edu/en/nav/ *

In these examples, students were asked to represent the number 31 in different ways.

31 represented with 31 ones
Students will typically count out 31 ones. Using this manipulative, the student simply clicks the one block 31 times. This example shows a student who understands one-to-one correspondence, but who may or may not understand the logic of the base ten system. This program does allow the students to go back and group the ones to make ten blocks.

31 represented with 3 ten blocks and 1 one block
This student clearly understands that 31 can be represented with 3 ten blocks and 1 one block. This student shows an understanding of how the base ten system works and what the two digits in the number 31 represent. Both this representation and the one to the left are important, and both accurately model the number 31.

31 represented with 2 ten blocks and 11 one blocks
This student has taken one of the ten blocks, and moved it to the ones place. When the ten block is moved, the ten is split up into ten ones. This reinforces to the students that tens are simply made up of ten ones. This program also allows students to merge ten ones back together again to make a ten block.

31 represented with 31 ones
The student can continue to drag tens to the ones place. It is clear to the student that each ten block moved to the ones place has split into ten ones. This understanding of grouping ones together to make a ten and splitting tens apart to make ten ones is crucial to students' understanding of the base ten system and imperative and for a clear understanding of regrouping when students move on to addition and subtraction.

Indicators:
6.1.1.1 model one- and two-digit whole
numbers using a variety of groupings.
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