Tape a shape onto your classroom floor. Use a simple shape, such as a square or rectangle. Make the shape large enough for your students to walk on. For example, you might create a rectangle that is approximately 4 feet long by 2 feet wide.
Explain to your students that you want them to walk on the tape of the shape on the floor. Ask them to count how many steps it takes to walk the entire distance of the shape's sides.
Write down your students' responses on the board. Measure the perimeter of the shape with a tape measure and compare the true calculation with the students' estimates.
Explain to your students that they just calculated a perimeter. Tell them that a perimeter is the length of all of the sides of a shape.
Draw various shapes on the board, and ask your students to tell you the perimeter. Write in measurements for each side of the shapes. Keep the numbers fairly low since first graders usually only have basic adding skills.
Give your students worksheets in which they must find the perimeter of various shapes. You can use these worksheets as classwork or homework.