An educational device is provided which can be used to teach arithmetic. The educational device comprises a track having a scale on an outer surface of said track. The scale is comprised of a plurality of evenly spaced apart unit markings, the markings being spaced apart by a unit length. Blocks are provided which are be slidingly received on the track. Each block has a length based on the unit length, and indicium is provided on the each block to identify the length of the block in unit lengths. When a set of blocks a positioned on the track, the end of the last block will line up with a unit marking on the scale representing the overall length of the set of blocks in "units", and hence showing the sum of the lengths of the set of blocks placed on the track. By adding and removing blocks to the track, addition and subtraction "facts" can be visually taught.