Start your students out by reviewing the shapes that they should already know: circle, square, rectangle, triangle. Discuss the similarities and differences. Build upon their knowledge by adding the less common forms to their vocabulary such as oval, pentagon, octagon, rhombus, parallelogram, cube, cylinder.
Play games that encourage your students to recognize the shapes with ease. Use flash cards and fun worksheets to give your students practice. Have a "geometry hunt" where everyday objects of various geometric shapes are planted around the classroom. The student to correctly identify the most shapes within a certain period of time wins.
Introduce the concept of area. Teach your students how to calculate area using shapes that are filled with equal-sized squares. Count the squares on one side and write the number. Do the same for the next side. Multiple the two and the answer equals the area. Bring in two-dimensional objects for them to measure and calculate the area such as a baseball card, square or rectangular piece of carpeting, and a cookie sheet.
Teach your students that the perimeter of a polygon is the measurement of the outside of the object. Show them that if they add the length of each side of the shape together, they will have found the perimeter of the object.
Move your students on to learning the difference between three types of triangles: right, acute and obtuse. Teach them that right triangles have one angle that is always a 90-degree angle. Explain that a 90-degree angle looks just like the corner of a square or rectangle. Give the definition of an acute triangle: All of the corners are less than 90 degrees. An obtuse triangle is a triangle in which one of the three angles is greater than 90 degrees.
Learning to calculate the area of a triangle is the next step. Have your students practice measuring the base and height of a triangle. Show them on the board that they should multiply the base times the height and then divide that answer by two to get the area of a triangle. Help them see how they can figure out the area of triangles found in everyday life. Give them practice pages with simple triangular objects such as the sail on a sailboat or a triangular slice of cheese. Ask them to calculate the area.