Tessellation is a cool topic in primary level to PSLE math. Most students will enjoy it even if they hate other types of Math. It is a natural human instinct to be amazed at how different shapes can fit together perfectly to tile the plane.
Apparently, tessellation is going to be removed from the entire PSLE syllabus soon (see http://schoolplus.com.sg/primary-math-syllabus-2017/). That is certainly quite sad for many reasons.
Triangles and quadrilaterals (even irregularly shaped ones) can be easily tessellated. However for pentagons, it is less clear and some pentagons (including the regular pentagon) cannot be tessellated!
For more information read the article here at: https://www.quantamagazine.org/the-math-problem-with-pentagons-20171211/