Double-check that your students understand the concepts of squaring a number and finding a square root by asking random students to solve simple problems such as "what is 9 squared?" Make sure they know the meaning of the terms "side," "hypotenuse" and "right triangle." Students should have confidence in these areas before moving on to more difficult material.
Introduce the concept of the Pythagorean theorem. Make sure that students understand that this is used to calculate the length of a side or hypotenuse of a triangle. Before asking students to solve "A squared + B squared = C squared," draw triangles with known values for A and B and ask students to explain how they would use that information to substitute values into the equation. For example, if side A is 4 inches and side B is 5 inches, the students should be able to substitute these values into the equation to read "16 + 25 = C squared."
Teach students to calculate the "C squared" value in the equation. Students should be able to square the length of sides A and B, and add them together to calculate C squared. Immediately after they get this value, emphasize taking the square root of their answer because the square foot of the calculated value is length of the side in question. For example, students should be able to (1) add 16 and 25 together, (2) take the square root of 41 and (3) identify that C is 6.4 inches long.
Drill students until they can confidently write the equation, substitute values into the equation, square the known values, add the squared values together and take the square root of the answer. This lends itself to drawing triangles on the blackboard and having kids shout out answers to questions about the length of the sides.