Goals:
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To promote discussion of students' ideas about decimals
for assessment and learning.
To enable students to self-correct their ordering of decimals
by size - using an area representation.
To promote discussion on ordering of decimals: why do we
consider digits from left to right?
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Year level:
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Grades 4 to 6
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Group size:
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This activity can be conducted as a whole class activity
or small groups of 6 students
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Equipment:
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Overhead transparency of the 'Area card sets' for a whole
class discussion (or alternatively the cards pasted on magnetic
strips for the board) .
Separate 'Area card sets' for small group work (6 students).
Each set contains 6 pairs of cards representing decimal
numbers. In each pair, there is one numerical representation
and one pictorial. Photocopy masters:
Area card set 1
Area card set 2
Area card set 3
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Time:
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10 - 20 minutes |
Activity Instructions:
1. The class is provided with 6 decimal number cards
which they order from largest to smallest. Emphasise that
there must be consensus and encourage students to express
their reservations about any ordering. Open discussion is
the key to making this activity effective.
2. Once number cards are ordered, put the cards to
one side preserving the order (the teacher has control of
this in a whole class activity).
3. Produce the corresponding picture cards and have
students order them from largest to smallest, based on the
amount of shading. (At this stage students do not know that
the decimal numbers and picture cards correspond.)
4. Students are then asked to compare their ordering
of the numbers to their ordering of the pictures - matching
up numbers and picture pairs and commenting on any changes
they would make and why.
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Comments:
The card sets are designed to create cognitive conflict,
hopefully leading to students with misconceptions (see Cases)
reconstructing their ideas about decimal notation.
Variations:
To promote discussion on alternate representations of the
same number, the final card set includes the numbers 2.2
and 2.20 represented pictorially as both 2 and 20 hundredths
and 2 and 2 tenths.
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