Geometiles Flexagons

The Geometiles Hexaflexagon
(or tri-hexaflexagon, to be precise)

The Geometiles Magic Wallet

The Geometiles Tetra-tetraflexagon

Wondering what the fake money is doing here? To make this work, you need a bill no more than about 2 inches (5 cm) wide.

Common Core State Standards and Geometiles activities

Title	Grade Level	Topics	CCSS
Tangrams	Grades 1+	Constructing 2-dimensional shapes	1.G.A.2
Shape Challenge, grade 2 and up	Grades 2+	Constructing polygons	2.G.A.1
Shape Challenge, grade 4 and up	Grades 4+	Constructing polygons; the 4th grade version reflects students’ familiarity with angles and classifying triangles.	3.G.A.1, 4.G.A.1, 4.G.A.2
Fractions	Grades 1 through 5	This sequence takes students from very basic understanding of fractions all the way through multiplying and dividing by fractions.	1.G.A.3, 2.G.A.2, 2.G.A.3, 3.NF.A.1, 3.NF.A.3, 4.NF.A.1, 4.NF.A.2, 4.NF.B.3, 4.NF.B.4, 5.NF
3D Solid Understanding	Grades 2+	Constructing and analyzing a rectangular and other prisms	1.G.A.2
Angle Mania	Grades 4+	Measuring angles, classifying triangles by angle types.	4.MD.C.5, 4.MD.C.7, 4.G.A.1, 4.G.A.2
Ratios plain and golden	Grades 6 through 8	Ratios and proportional relationships; Golden Ratio.	6.RP.A.1, 7.RP.A.2
Volume and Cavalieri's Principle	Grades 6 through 8	Volume and surface area.	HSG.GMD.A1, HSG.GMD.A2, HSG.GMD.A3
Triangles: similar, special, and right	Grades 8+	Similar polygons, special triangles, Pythagorean Theorem, irrational numbers.	8.NS, 8.G.A.4, 8.G.B.6, 8.G.B.7
Platonic and Archimedean Solids	Grades 1+	Platonic and Archimedean solids	Enrichment topic