# Perimeter

by on March 22, 2011

As in any new skill, a key to learning a concept such as Perimeter is to help your second grade children see how these math concepts can be useful in everyday life. As much as possible, try to reinforce these second grade math concepts as you see the opportunity to do so throughout your day. You’ll see where I’ve suggested a few ideas on how to do this later in the post.

What is Perimeter?

The perimeter is the distance around the edge of a figure.

Tips/Activities:

• Perimeter is more concrete than the concept of Area.  I like to have kids walk around the perimeter of things to get the idea that it really is a measure of distance AROUND something.  For example, you could ask your child to walk around the outside of your house, as close to the house as possible.  Or, she could walk around a room, as close to the walls as possible.
• Due to the fact that many children confuse the terms perimeter and area, I have a little trick to help them remember what the perimeter is. I say the word perimeter in syllables PE – RIM – E – TER, and as I say each syllable, I draw the side of an object such as a rectangle.  By the time I get to the 4th side, I have finished the word.  Of course, you can find the perimeter of shapes with a different number of sides than 4, but we usually begin with 4-sided shapes, so this trick sticks in their minds.
• Your child will begin exploring perimeter with simple 4-sided shapes such as squares or rectangles.  For example, she will be given this shape with measurements on each side:

Tell your child to pretend that a little ant is going to walk around the rectangle.  Have her decide in which corner the ant will begin.  She can move her fingers around the rectangle to trace the ant’s steps.  If she begins in the upper left-hand corner, she would walk along the top side and say 8 cm.  Then she would walk down the right side and say 2cm.  Then she would walk along the bottom side and say 8 cm again, and finally up the right side and say 2cm.  Ask her how she can figure out how far the ant went altogether.  She may be able to add all 4 sides in her head, or she may write the numbers down.  The answer would be that the perimeter = 20cm.

• Once your child has been exposed to many different shapes with the lengths of the sides given, she will be ready to measure each side on her own to calculate the perimeter.  She will be given a shape with 3, 4, or more sides, and she will need to use her ruler to measure each side.  Remind her to write down the measure of each side on the shape itself.  She will then add up all the sides as she did previously.
• If your child is having trouble understanding why she is adding up all the sides to find the perimeter of a shape, try taking a string and putting it around the perimeter of a book (for example). At each corner of the book, take a marker and mark a line on the string.  You should have 4 marks.  Using her ruler, ask your child to measure each side of the book while the string is still around its perimeter.  Record the lengths of each side.  Now remove the string and lay it out on the floor or table.  Show her the lines that she made to represent each side.  Lay a yardstick or tape measure down next to the string to measure the whole length of the string.  She will see that all the sides added up make one longer length, which is the perimeter.
• Try to give real-life examples of perimeter.  Tell her if you were getting a dog, you might want to put a fence around your yard.  When the fence company comes to your house, they will need to calculate the perimeter of your whole yard to determine how much fencing is needed to completely enclose your yard.  You could extend this with older students by researching how much fencing costs per foot; then have your child calculate the perimeter of the yard and figure out the cost of a fence!

What to watch for:

• Perimeter and Area are often taught together, and many children confuse the two terms.
• The unit of measure for perimeter is straight inches, centimeters, feet, yards, meters, miles, kilometers, etc. Children often forget to put the unit after they measure the perimeter.
• If your child has a rectangle to measure, she will eventually see that the opposite sides of the rectangle have the same measurement, so she will not actually need to measure every side.  Watch for this development in your child. It’s a second grade math skill that will usually occur a little later in the year.
• Sometimes perimeter is taught by drawing shapes on grid paper.  This can be confusing to children, because they want to count the squares (as you would for Area).

WANT MORE?

• As always, playing math games at home is a great way to reinforce math skills learned in school.