lesson has two parts. The first part involves estimation of area, and
the second part involves actually measuring the area for accuracy. The
parts can be completed separately, or students can be given all the
information up front and allowed to work at their own pace.
To prepare for the estimated area activity, you may want to
measure ahead of time various items in your classroom that you could
suggest to students as measurement reference points. The Area Contractor
Activity Sheet is set up to include a typical classroom with 4 walls
and standard obstructions. Modifications may necessary for rooms with a
different number of walls or unique architecture.
Divide students into groups of three and assign roles. Each
group member should be assigned a task role and a measurement role, as
outlined on the activity sheet. This lesson lends itself to
differentiated instruction through group role assignments (see
discussion below). Groups will indicate their assigned roles on their
activity sheets by circling their role titles.
Part 1: Estimation
Each group must first estimate the surface area of the classroom
walls and floor using reference points found in the classroom. If
students are not familiar with estimating measurements using reference
points, you may want to consider the following questions as a way to
access prior knowledge or help identify potential reference points in
- What is the difference between estimation of area and actual area?
[Estimation is based on visual inspection and reference
points. For example, to estimate the area of a wall, use visual
inspection to count the number of concrete blocks, 8” by 16”. Actual
area requires the use of a tape measure with accuracy within prescribed
- What reference points in the room could you use to estimate
the gross square footage of the ceiling, walls, and floor of the
[Standard door height is 80” or 6’8”. Concrete (cinder)
blocks are 8” by 16”. Floor tiles are typically 12” square. Other
reference points might include bookcases, counter tops, desks, and
students’ physical height.]
During the estimation phase, actual measuring instruments are not to
be used. Estimations are to be checked by each member of the group for
reasonableness before proceeding with actual measurements. While
students work on their estimations, you might want to consider posing
one or more of the following questions to group members:
- What reference points did you use to derive your estimate?
[Reference points that students might choose could include
their personal heights, bookcases, desks, bricks, doors, or windows.
Some doors have height labeled, so they may choose those.]
- Why did you choose these reference points?
[Most students will tell you that they “know those
measurements” or it just makes sense to them. Be prepared for some
- How close do you think your estimate is to the actual measurement? Why do you think this?
[The majority of students will be over on their estimates,
which is a reasonable result. When asked why, they will tell you they
either guessed or rounded up. If their measurements are under, the
typical explanation is that they could not reach. Estimates can also be
under the actual measurements if students did not properly convert
their units between inches and feet.]
Part 2: Accurate Measurement
It is important that students know how to properly use and read
a tape measure. If students are completing both parts of this lesson at
their own pace, you may want to instruct them on how to use the tape
measure before they begin Part 1, the estimation activity. If all
groups start Part 2 at the same time, it would be better to instruct
students on how to use the tape immediately before the accurate
Each person in a group will use the measuring tapes provided to
measure the surface area of one or more classroom walls and floor for
accuracy. Measurements are to be reviewed by each member of the group
for reasonableness. If there is a question of reasonableness, then the
surface in question should be measured again by a different group
member. If time permits, have someone else within the group verify all
measurements for accuracy. As students work on collecting their actual
measurements, consider asking group members one or more of the
- How close were you to your original estimate? What might have accounted for the difference?
[Answers will vary regarding closeness. Many differences
tend to be from conversion between inches and feet, recording
measurements incorrectly, or not paying attention to detail.]
- If you were going to paint this wall, do you think it is important to actually measure it or would an estimate been good enough?
[Most students will tell you that an estimate is good
enough, and if they ran out of paint they would just buy more. This is
true for many do-it-yourself projects, but if a contractor had to buy
more paint, he/she would lose money. A contractor would have first bid
on the job for a specific number of hours and amount of paint. If it
takes longer or takes more paint, it costs the contractor, not the
customer, more money.]
Have groups prepare a presentation to the class comparing their
estimates to their actual measurements. Presentations should include
the methods the group used for their estimates and a discussion of why
there is a difference between the estimate and the actual measurement.
Once all groups have presented their findings, consider a whole-group
discussion using one or more of the Questions for Students.
This activity can be used with differentiated instruction and
mixed-ability groups. Each student within a group will have an assigned
role. You or the group members can make these assignments. If you
assign the specific roles within a group, consider doing so based on
the students’ ability levels.
Level 1 – The Novice of the group should be assigned the responsibility of measuring the wall with minimal obstructions.
Level 2 – The Apprentice should have proven skills in estimating
and measuring area. The apprentice should be assigned the
responsibility of measuring the wall with simple obstructions, such as
Level 3 – The Expert should be assigned the task of determining
the net surface area of walls with complex obstructions. Complex
obstructions may include multiple windows, doors, or cabinets.