Rekenrek: Free Online Rekenrek With 20 and 100 Beads

What a rekenrek teaches

A rekenrek helps young children stop counting by ones. On a plain row of ten beads, a child has to count to find 7. On a rekenrek, 7 is all five red beads and two white beads, and after a little practice the child simply sees it. That shift, from counting every object to seeing groups, is the start of number sense.

The rack is simple: each row has ten beads, five red and five white. On the 20-bead rack there are two rows; on the 100-bead rack, ten. Beads start on the right, and only the beads slid to the left count. The name is Dutch for "calculating frame," and the tool is part of the family of red-and-white counting frames used in primary schools.

Two structures do the work:

• Five. The color change at 5 means any number from 6 to 10 is "five and some more." 8 is 5 and 3; 9 is 5 and 4.
• Ten. A full row is 10, so 13 on the 20-bead rack is a full top row and 3 on the bottom.

How to use this online rekenrek

Tap a bead to slide it to the left, and every bead before it goes too, in one push. That is how teachers use real racks: "Show me 7 in one push" means pushing the first seven beads together, not counting seven separate beads. Tap a bead on the left to send it and the beads after it back.

• Show a number. Type it into Show, or push beads yourself. The readout gives each row and the total.
• Read the structure. The readout notes "8 is 5 and 3 more" or "Make ten: 8 + 2 = 10, and 3 more is 13."
• Quick look. The rack flashes a number for a moment, covers it, and asks how many. Children who answer without counting are using the fives and tens.
• Hide value. Turn the readout off so children have to say the number themselves, then show it to check.

Making ten, doubles and near doubles

The 20-bead rekenrek is built for the addition strategies first graders learn. The Common Core standards ask kindergartners to find the number that makes 10 with any number from 1 to 9 (K.OA.A.4) and first graders to add and subtract within 20 using strategies such as making ten and doubles (1.OA.C.6). Second graders add and subtract within 20 fluently, knowing all sums of two one-digit numbers from memory by the end of the year (2.OA.B.2).

Task card 7 shows 9 + 4 and asks for the same total as 10 + something: the child slides one bead back on the bottom row and one more onto the top row, and 9 + 4 becomes 10 + 3. That move is exactly the mental step behind the making-ten strategy.

The 100-bead rekenrek

The 100-bead rack has ten rows of ten. Every full row is a ten, so 47 is four full rows and seven beads on the fifth. The board leaves a slightly larger gap after the fifth row, which helps children see 50 as the top half. Use it to count by tens (1.NBT.C.5 asks first graders to find 10 more and 10 less mentally), to see that 36 and 10 more is 46, and to add within 100 by finishing a row: 68 + 5 is 2 more to 70 and 3 more.

Rekenreks by grade

Activities to try

• One push. Call out a number from 1 to 10. Children show it with a single push and say how they knew where to push. (For 8: "all the red and three white.")
• Flash and tell. Use Quick look. After each answer, ask "how did you see it?" Some children see 7 as 5 and 2; others as 10 take away 3. Both are useful.
• Partners of 10. Show a number on the top row. How many beads are still on the right? That's its partner.
• Two ways to make 8. Show 8 on one row, then on two rows in as many ways as you can: 4 and 4, 5 and 3, 6 and 2.
• Doubles to near doubles. Show 5 + 5, then slide one more on the bottom: 5 + 6 is one more than the double.
• Tens race. On the 100-bead rack, start at any number and add a ten each turn. What stays the same?

Tips for teachers and parents

• Push, don't count. Encourage children to move beads in groups. If a child slides one bead at a time, ask them to show the number in fewer pushes.
• Ask how they saw it. NCTM's teaching practices emphasize discussion of strategies. Two children who both answered 9 may have seen it differently, and comparing those views is where the learning happens.
• Use the rekenrek with ten frames. The rekenrek and the ten frame share the same 5 and 10 structure. Children who move between them see that the structure matters, not the tool.
• Then move to the abacus. Once children think in fives and tens, an abacus adds place value: a bead on the next rod is worth ten.

What makes this rekenrek different

This rekenrek moves beads the way real racks do, in one push from the bead you tap. It adds both racks, a row-by-row readout with number sentences, making-ten, doubles and near-doubles notes, Quick look flashes, Show for any number, pen and text labels, undo and redo, share links, a printable snapshot, keyboard controls, and sixteen self-checking task cards across the two racks. It runs in any browser, with no account.

Some math programs are built around groups of five and ten; RightStart Mathematics, for example, teaches its early lessons on an abacus grouped that way. Compare options in the best kindergarten math curriculum guide, and print addition worksheets for practice on paper.