1
U n t er r i ch t spl a n
Id e nt if y Po l y g o ns and F ind
Pe rime t e r
Altersgruppe: 3 r d Gr ade , 4 t h Gr ade , 5 t h Gr ade
Mathematics Syllabus Primary : 3 .M .A P .1, 3 .M .A P .2, 3 .M .A P .4 ,
3 .M .A P .6, 5 .F M - M .A P .1, 5 .F M - M .A P .5
Online-Ressourcen: P e r i me t r i c I I
Opening
T eacher
present s
St udent s
play
Class
discussion
15
15
10
10
min
min
min
min
ZIE L E :
E x pe r i e nc e finding perimeter using arbitrary units
P r ac t i c e identifying polygons by name
L e ar n to strategies rotate polygons to measure side lengths
De v e l o p strategies for finding perimeter, such as using
symmetry
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2
Ope ni ng | 15 min
Draw or project various polygons on the board.
Ask the students to identify the polygons, being sure to ask, “How
else could we describe this shape?” or “What else could we call this
shape?” in situations where a shape may fit under several categories
(e.g., a rectangle is also a parallelogram).
Draw or project polygons with side lengths already provided.
Ask the students to find the perimeter of the shapes shown.
It is important to discuss the different ways that students arrived
at their answers, in order to develop and strengthen strategies.
As a challenge, consider providing only some of the side lengths,
where the missing side lengths can be determined based on traits
like congruence.
T e ac he r pr e se nt s A l l t he W ay A r o und: I de nt i f y and
M e asur e | 15 min
Present Matific ’s episode A l l t he W ay A r o und - I de nt i f y and
M e asur e to the class, using the projector. The goal of this
episode is to find the perimeter of various polygons, with the added
element of identifying the correct polygon from the three given.
E x a m p le :
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3
First, have the
students identify
which of the
three shapes is
named in the
question.
If they do not
come to a
consensus, click
on the name on
the polygon (in
blue). A small
pop-up will
provide several other shapes by the same name.
E x a m p le :
Once the
correct
shape is
chosen,
ask the
students
what the
perimeter
is, in
general.
Then, ask
the
students
how to
find the
perimeter of the chosen shape.
Show the students that you can move and rotate the shape. Move
the shape as needed in order to measure the side lengths in arbitrary
“units.”
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Some side lengths may not appear to be exactly a whole number
of units.
E x a m p le :
As the sides
are measured,
have the
students keep
track of the
individual
lengths.
Finally, ask the
class how to
find the
perimeter of
the figure.
The episode will present a total of six questions.
S t ude nt s pl ay A l l t he W ay A r o und: I de nt i f y and M e asur e |
10 min
Have the students play A l l t he W ay A r o und - I de nt i f y and
M e asur e on their personal devices.
Circulate, answering questions. Continue to promote more efficient
and creative strategies for finding perimeter.
Be aware of the potential confusion between finding area and
finding perimeter.
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5
C l ass di sc ussi o n | 10 min
Ask the students if they discovered or developed any notable
strategies for finding perimeter.
Work with the students to create and walk through some
examples of these strategies.
Present several polygons with missing sides, and discuss whether
or not the missing side lengths (and, hence, the perimeter) can be
found or approximated.
E x a m p le s :
Missing side lengths can be found exactly using properties of rectangles.
The missing side length is greater than 4, but there is not enough information
to conclude much more than that.
Ask the students whether it is fair to assume certain attributes, like
whether all sides of a pentagon are congruent. Show one example
where the sides are congruent and one where they obviously are not.
Work on some perimeter examples that involve real-life scenarios,
such as finding the distance around a house.
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