A tessellation is pattern that is repeated with shapes that fir together with no gaps over overlaps. Not all shapes are able to tessellate. As an introduction to the topic in the classroom the children should have access to shapes that will and will not tessellate so they can work out for themselves which ones will tessellate. The next step is to find out why some shapes tessellate when others do not. Shapes such as rhombus, square, equilateral triangle and hexagon can tessellate. This is because the angles within these shapes fit a vertex to give 360° or in the case of  the triangle 180°. Some shapes that do not tessellate include pentagons and octagons. The internal angle of a pentagon is 110° therefore three fitted together is 330° and leaves a 30° gap in the vertex. The internal angle of an octagon is 135° therefore three together is 405° and causes an overlay in the vertex. After children have mastered the skill of tessellating these simple shapes they can move on to Escher style tessellating. An example of this can be seen in the following video: