This page contains a collection of some of the best free Geometry teacher lesson plans from around the web. Great for use by teachers or homeschool parents!
The Coordinate Plane  Graphing Points 
Geometry Lesson Plan

"In this lesson, students will have the opportunity to learn the basics of coordinate graphing and practice plotting points on the coordinate axis". This lesson plan is organized as follows: 1. Graphing quiz, 2. Introduction to the coordinate plane and coordinates, 3. Coordinate Game, 4. Maze Game, 5. Written Report. 
Quadrilaterals in the Coordinate Plane

Geometry Lesson Plan

In this lesson, "Students will be able to apply definitions and theorems to verify special quadrilaterals using coordinate geometry." This lesson plan consists of a warmup activity on slope then a main lesson where students must apply the slope formula, midpoint formula, and the distance formula to justify that a quadrilateral is a parallelogram given the coordinates of its vertices. This lesson plan contains two worksheets and a formula sheet handout.

Unit Plan: Measuring Up

Geometry Lesson Plan

This unit lesson plan "explores the concepts of proportional reasoning, ratio, and indirect measurement. Students engage in a variety of activities that involve taking their own measurements, exploring different ratios, and examining similar figures. Students convert measurements into customary and metric units. These activities immerse students in problem solving, reasoning, and making connections to reallife situations". This unit plan consists of the following individual lessons:

Deductive and Inductive Reasoning 
Geometry Lesson Plan

"Maybe youÃ¢â‚¬â„¢ve seen Dr. House in action Ã¢â‚¬â€œ figuring things out from what seem like totally unrelated clues. Like Sherlock Holmes before him, House is a master of induction. In this lesson, students will keep up with the doctor (and a lawyer, too) as they learn how to spot Ã¢â‚¬â€œ and analyze Ã¢â‚¬â€œ both inductive and deductive arguments. Students will then get a chance to show off their deductive skills by solving a logic puzzle and test their inductive abilities by solving a 5minute mystery". 
Pieces of Proof

Geometry Lesson Plan

"There is a leap to be made from understanding postulates and theorems in geometry to writing proofs using them. This lesson offers an intermediate step, in which students put together the statements and reasons to build a formal proof." This great lesson plan includes a handout containing six sample proofs. 
Transformations  Reflections & Dilations 
Geometry Lesson Plan

"Students will be able to identify and compare the three congruence transformations, apply the three congruence transformations to coordinates of the vertices of figures, identify and apply dilations, and apply transformations to realworld situations." This lesson plan includes three worksheets: Reflections over Two Lines, Dilations using Measurement, and Transformations.

Squares, Diagonals, and Square Roots

Geometry Lesson Plan

This lesson plan is on the "relationship between the lengths of the sides and diagonals of a square. Students will use their discoveries to predict the diagonal length of any square". This lesson plan contains worksheets, questions for students, assessment options, and extensions.

Rectangles, Diagonals  Pythagorean Theorem 
Geometry Lesson Plan

In this lesson, "students explore square roots using the diagonals of rectangles. Using measurement, students will discover a method for finding the diagonal of any rectangle when the length and width are known, which leads to the Pythagorean Theorem". This lesson plan contains worksheets, questions for students, assessment options, and extensions. 
Triangle Angle Sum Theorem 
Geometry Lesson Plan

This lesson plan is on the Triangle Angle Sum Theorem. Objectives include: "Review some properties of angles and lines, explore some properties of triangles, and prove the Triangle Sum Theorem". This lesson plan requires GSP for lab activity. 
Fun with Angles (Formed by Parallel Lines) 
Geometry Lesson Plan

This lesson plan will help the students visualize the different angles (corresponding, alternate interior, and sameside interior) when coplanar lines are cut by a transversal. 
Angles and Parallel Lines 
Geometry Lesson Plan

This lesson plan introduces the concept of supplementary angles formed by a line that transverses two parallel lines. This plan consists of an "attention getter", activities, review activities, assessment, and a supplemental challenge. A total of nine worksheet pages are included. 
Congruent Triangles  Is This Enough Information? 
Geometry Lesson Plan 
This is a 4 day (172 minute) lesson plan on congruent triangles and triangle congruence postulates (SSS, SAS, ASA, AAS, HL, and CPCTC). "Goal: Students will learn about some of the congruence postulates and apply the knowledge to triangles in the world around them." The link above takes you to a page containing this lesson plan. Click here for a direct link to the lesson plan PDF file (requires Adobe Reader). 
Triangle Congruency Theorems & Fettuccine

Geometry Lesson Plan

In this lesson, "the students will use fettuccine noodles to discover the truth of different conjectures about triangle congruencies. They will develop an understanding of the triangle congruency theorems that will be used throughout geometry. A problem involving needing to find congruent triangles will be posed and students will begin with the most basic case and work toward the actual congruency theorems in solving this problem." 
Similar Triangles and Similarity Postulates

Geometry Lesson Plan

This multiday lesson plan is on similar triangles and the postulates and theorems relating to them (AA, SSS, and SAS). In this lesson, students will calculate lengths using properties of similar triangles, solve proportions, and explain the theorem or postulate that allows the triangles in a problem to be similar. The goal of the lesson: "to find the height of different objects such as a tree or the flagpole in the front of the school". The link above takes you to a page containing this lesson plan. Click here for a direct link to the lesson plan PDF file (requires Adobe Reader). 
Inequalities in Triangles

Geometry Lesson Plan

This is an outstanding lesson plan on Inequalities in Triangles. From the lesson, "Students will use pasta to create models of triangles and nontriangles and investigate the relationship between the longest side of the triangle and the sum of the other two sides of the triangle. In addition, students will measure the sides and angles of a scalene triangle and investigate the relationship between the location of the largest angle and largest side in a triangle." This complete lesson includes two activity worksheets (The Triangle Inequality and Inequalities for Sides and Angles), examples, assessment, and extensions. 
Trigonometry Puzzles 
Geometry Lesson Plan

"This lesson offers a pair of puzzles to enforce the skills of identifying equivalent trigonometric expressons. Addtional worksheets enhance students' abilities to appreciate and use trigonometry as a tool in problem solving". In the first puzzle, students apply trig values for some common angles. In the second, students use trig identies to match equivalent expressions. 
Polygon Capture Game

Geometry Lesson Plan

This is a great lesson plan for teaching students to describe, classify, and understand relationships among types of polygons. From the lesson, "students classify polygons according to more than one property at a time. In the context of a game, students move from a simple description of shapes to an analysis of how properties are related". This lesson plan includes all necessary handouts and worksheets and includes extensions. 
Polygons  Sorting by Attributes 
Geometry Lesson Plan

"Students identify and classify polygons according to various attributes. They then sort the polygons in Venn Diagrams, according to these attributes. Extensions to fundamental ideas about probability and statistics are also included." . 
Polygons  Sum of Interior and Exterior Angles

Geometry Lesson Plan

In this lesson, students will learn to find the sum of the interior and exterior angles of any polygon and to construct a polygon and its exterior angles given the number of sides. 
Angles, Polygons, Pythagorean Theorem, Basic Trig 
Geometry Lesson Plan

This page contains five separate lesson plans:
 Lesson Plan 1: To identify and apply common properties of triangles, special quadrilaterals, and ngons.
 Lesson Plan 2: To define and illustrate terms related to polygons, to classify quadrilaterals and polygons, to construct types of parallelograms, and to state and apply properties of parallelograms.
 Lesson Plan 3: To determine the sum of the measures of the interior and exterior angles of a convex polygon of n sides and to determine the measure of a central angle of a polygon.
 Lesson Plan 4: To calculate the length of a missing side of a right triangle using the Pythagorean Theorem, to use the converse of the Pythagorean Theorem, and to solve word problems.
 Lesson Plan 5: To calculate the measure of an angle or the length of a side of a right triangle using the tangent, sine, and cosine ratios.

Measuring the Earth

Geometry Lesson Plan

In this lesson, you will repeat Eratosthenes' experiment of measuring the circumference of the earth using trig and the angle of elevation of the sun at noon. This lesson requires cooperation of another math class located north or south of your location. Click here for more information on Eratosthenes and how to measure the the size of the earth. 
Area, Surface Area, and Volume 
Geometry Lesson Plan

This multiday lesson plan is on Area, Surface Area, and Volume. From the lesson plan: "The overall goal is for students to demonstrate application of area, surface, and volume in the world around us. Students will apply formulas to a model of the classroom so they can determine the volume and surface area of the room". Students will be able to calculate the area, surface area, and volume of 2 and 3dimensional geometric shapes. The link above takes you to a page containing this lesson plan. Click here for a direct link to the lesson plan PDF file (requires Adobe Reader). 
Liquid Volume

Geometry Lesson Plan

In this lesson, students will use the formulas for volume of rectangular prisms and cylinders and see the relationship between cubic centimeters and milliliters. 
Exploring Similarity Using Scale Drawings

Geometry Lesson Plan

This lesson plan is on exploring the properties of similarity using models and scale factor. Students will "calculate surface area and volume for the original and the scaled down rectangular solids and calculate and interpret scale factors for length, area and volume of two similar objects". 
Discovering Pi 
Geometry Lesson Plan

This lesson plan is on discovering pi. In this lesson, students will "measure the circumference of an object to the nearest millimeter, measure the diameter of an object to the nearest millimeter, explain how the number 3.14 for pi was determined, demonstrate that by dividing the circumference of an object by its diameter you end up with pi, and discover the formula for finding circumference using pi, and demonstrate it. 
Circle Packing 
Geometry Lesson Plan

"In this unit, students explore circles. In the first lesson students apply the concepts of area and circumference to explore arrangements for soda cans that lead to a more efficient package. They then experiment with threedimensional arrangements to discover the effect of gravity on the arrangement of soda cans in the second lesson. The final lesson allows students to examine the more advanced mathematical concept of curvature." 
Exploring Geometry on the Sphere

Geometry Lesson Plan

This lesson plan is on spherical geometry. Students will learn vocabulary such as great circle, geodesic, spherical angle, and spherical triangle and how to measure spherical angles. 
Spherical Geometry  A Global Perspective 
Geometry Lesson Plan

This lesson plan provides a very good introduction to spherical geometry. Students will "relate prior knowledge about the globe to definitions and properties in spherical geometry and given a common definition or property in Euclidean geometry, make a conjecture about the corresponding statement in spherical geometry." 