Similar Triangles is a task created for geometry students learning how to determine if triangles are similar based off of side lengths. Students are given two triangles and the lengths of every side and must construct an argument as to whether they are similar or not. Sentence starters and argumentation language are provided to encourage a claim and the use of evidence.

Microsoft Word version: 912Geometry_SRT_SimilarTriangles_Worksheet_Construct_SimilarTriangles

PDF version: 912Geometry_SRT_SimilarTriangles_Worksheet_Construct_SimilarTriangles


Not in my Backyard is a task developed for geometry students learning about similar triangles. The task asks students to critique a student’s argument that two triangles are similar. Students must construct an argument and the task uses argumentation language including claim and evidence. The task suggests having students use the argument writing frame first, then constructing the argument. The task addresses a common misconception about similar triangles, that if you add the same number to each side and get the other triangle, then triangles are similar. Students must know the difference between proportions and differences.

Microsoft Word version: 912Geometry_SRT_SimilarTriangles_Worksheet_ConstructCritique_NotinmyBackyard

PDF version: 912Geometry_SRT_SimilarTriangles_Worksheet_ConstructCritique_NotinmyBackyard


The Rotation Exploration is a task designed for geometry students learning about rotations. Students are given a conjecture about rotations claiming that the only point that stays stationary is the center of rotation. To aid in the development of an argument agreeing or disagreeing with the conjecture, students are to define vocab words, gather data, form a hypothesis, and construct an argument. Examples are given for students to gather data from and sentence starters and a checklist are provided to help with the development of a strong mathematical argument.

Microsoft Word version: 912Geometry_CO_Rotations_Worksheet_Construct_TheRotationExploration

PDF version: 912Geometry_CO_Rotations_Worksheet_Construct_TheRotationExploration


Julia’s Reflections is a task used in geometry classes when working with geometric reflections within the coordinate plane. This worksheet has students using knowledge about reflections and transformations on the coordinate grid to critique an argument about how the reflection over the line y=x transforms a figure. Students must write an argument that either agrees with or disagrees with the statement given on the worksheet.

Microsoft Word version: 912Geometry_CO_Reflections_Worksheet_ConstructCritique_JuliasReflections

PDF version: 912Geometry_CO_Reflections_Worksheet_ConstructCritique_JuliasReflections


Casting Shadows is a task on similar triangles for geometry students. In the problem, one fourth grader knows his height and shadow length and wants to use similar triangles to determine another fourth grader’s height, when only knowing the shadow length. Students are to critique the proof given on the height of the other fourth grader and construct their own response, using a template, claim, evidence and warrants.

Microsoft Word version: 912Geometry_SRT_SimilarTriangles_Worksheet_ConstructCritique_CastingShadows

PDF version: 912Geometry_SRT_SimilarTriangles_Worksheet_ConstructCritique_CastingShadows


Parallel Lines is a task developed for geometry students studying properties of parallel and perpendicular lines. Students must be able to construct perpendicular lines, given a set of guidelines, and determine if the lines drawn are parallel. Students must construct an argument by stating a claim and providing evidence and support. The task offers a template for students to create an argument by providing sentence starters for each piece of the argument.

Microsoft Word version: 912Geometry_ParallelLines_Worksheet_Construct_ParallelLines

PDF version: 912Geometry_ParallelLines_Worksheet_Construct_ParallelLines


Critiquing Reasoning Problems is a task created for geometry students learning about corresponding angles. Students are given four problems and must either construct an argument or critique another’s reasoning with a claim and evidence. Vocabulary such as alternate-exterior angles, same-side exterior angles, and linear pair are used, alongside pictures and proofs to supplement the questions.

Microsoft Word version: 912Geometry_CorrAngles_Warmup_ConstructCritique_CritiquingReasoningProblems

PDF version: 912Geometry_CorrAngles_Warmup_ConstructCritique_CritiquingReasoningProblems


Vertical Angles is a task designed for geometry students learning about properties of angles and congruence. The task also works as a good exercise for students to critique arguments and determine what makes a good argument. The task looks specifically at two arguments that must prove why all vertical angles are congruent. Students must recognize that you need more than examples in order to prove a statement. Students are asked to contruct their own arguments after critiquing others.

Microsoft Word version: 912Geometry_VertAngles_Worksheet_ConstructCritique_VerticalAngles

PDF version: 912Geometry_VertAngles_Worksheet_ConstructCritique_VerticalAngles

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A template of the talk frame was used to plan a geometry lesson on supplementary angles. The teacher recorded a paraphrased version of the question in the Think section, what ideas would be contributed in the Talk Ideas section, and the realization that linear pairs are formed at the intersection of two lines. Students are asked to name pairs of supplementary angles and construct an argument to convince another person that the claim in true.

Microsoft Word version: 912Geometry_SuppAngles_LessonPlan_Construct

PDF version: 912Geometry_SuppAngles_LessonPlan_Construct


This task is designed for geometry students to display knowledge of the properties of different angles. Students must be able to recognize what makes angles both supplementary and complementary. Given a complex visual of multiple intersecting lines and a select few angle measures, students must determine which angles are supplementary and be able to contruct an argument as to why angles are supplementary.

Microsoft Word version: 912Geometry_SuppAngles_Worksheet_Construct

PDF version: 912Geometry_SuppAngles_Worksheet_Construct