Abstract: A teaching aid including a face panel having a flat front chamber and a plurality of squares defined within the flat front chamber and marked with a respective mark, a partition panel fitted into the flat chamber of the face panel and having a plurality of slots corresponding to the squares of the face panel, a set of mother blocks adapted for fitting into the slots of the partition panel, each mother block having an insertion hole of a particular design, and a set of differently shaped daughter blocks adapted for fitting into the insertion holes of the mother blocks respectively.