Illustrative Mathematics
The Geometry of Letters
Use the alphabet as a tool for teaching your class about geometric figures. Break apart capital letters into line segments and arcs. Classify angles as right, acute, or obtuse. Identify parallel and perpendicular lines. An excellent...
Illustrative Mathematics
All vs. Only Some
All shapes have certain defining attributes that set them apart from others. In order to understand this, young mathematicians look at examples and non-examples of triangles, rectangles, and squares, working as a whole class to create...
Illustrative Mathematics
Are These Right?
Is that a right triangle or a wrong triangle? Young mathematicians look at eleven different shapes and use a measuring tool of their choice to determine which triangles have right angles. Consider cutting out sets of the shapes to...
Education Development Center
Finding Parallelogram Vertices
Four is the perfect number—if you're talking about parallelograms. Scholars determine a possible fourth vertex of a parallelogram in the coordinate plane given the coordinates of three vertices. They read a conversation...
Texas Instruments
Texas Instruments: Classifying Triangles by the Length of the Sides Using Cabri
This activity uses Cabri Jr. to classify triangles according to the length of their sides. [Requires Adobe Reader.]
National Council of Teachers of Mathematics
Nctm: Illuminations: Cutting Corners
Students will use their knowledge of plane figure attributes to create and view shapes by cutting and rotating shapes to stimulate discussions on names and attributes of various shapes they do not regularly encounter.
Beacon Learning Center
Beacon Learning Center: Triangles Side by Side
This comprehensive web lesson describes how to classify triangles by their angle and side measurements. It provides real-world examples and exercises for students to practice the skill.
NumberNut
Number Nut: Shapes, Symbols, and Colors: 2 D Shapes
Did you know that two-dimensional shapes are also called polygons? This lesson describes the various 2-D shapes and includes two interactive games to reinforce skills.
NumberNut
Number Nut: Shapes, Symbols and Colors: Two Dimensional Shapes
Describes, with illustrations, the basic two-dimensional shapes students will encounter in elementary Math.