The 20 Bead Teacher & Student Abacus (sometimes called Arithmetic Racks) are idea resources to introduce children to the five and ten structure of numbers. Using these numbers as reference points, children can combine and partition numbers to investigate efficent strategies for counting, addition and subtraction.

Children who are fluent with five and ten as reference points are unlikely to rely on long sequences of counting-by-ones when adding or subtracting.
Robert, Wright J., et al.(2006). Teaching Number in the Classroom

Both frames and beads are made from solid wood, the rods are stainless steel .

The 20 Bead Teacher Abacus is an ideal size for demonstrating concepts to the whole class.
Frame size 120 x 520mm. Wooden beads 36 x 22mm.

The 20 Bead Student Abacus is perfect for individual use to practice and extend concepts demonstrated by the teacher.
Frame size 73 x 256mm. Wooden beads 20 x 11mm.

Extend to numbers to 100 using the Giant Teacher Abacus.