The Hundred Board

A hundred squares, ten to a row. Count on from where you are.

Game Place value to 100 1.NBT.A.11.NBT.B.21.NBT.C.5 MagPI · Number line estimation ALPACA · Early operations

Counting on in ones? Start here. A short lesson on a number line, where one marker jumps ten at a time so you can see that every jump of ten is the same size. About about 4 minutes.

Show me jumps of ten → How do jumps of ten work again?

▤ Print this All of 1st grade

For grown-ups

How long: 5 to 10 minutes is plenty. Short and frequent beats long and occasional — the early-numeracy trials with the largest effects ran eight weeks or less.
The strategy to reinforce: “Count on” — Start on the number you are already on and count on. On 38 and spinning 3? Say “thirty-nine, forty, forty-one”. If they stall, remind them of this rather than giving the answer.
When they get one wrong: the page shows the working. Read it together rather than moving straight on. Feedback that explains is worth several times more than feedback that only marks right or wrong, and that gap is wider in maths than in any other subject.
On the timer: it is off unless you turn it on, and it is never needed. Use it only once the skill is comfortable, never to introduce it.
Print it too: doing the same problems on paper a few days later is worth more than doing twice as many today.

What this practises

Counting on across a ten, on a board where the tens are rows and the ones are columns.

The linear board game is the strongest causal result in early number — Siegler and Ramani (2009) found number-line error dropping from 29% to 21% after about an hour of play, and the same game on a circular board did almost nothing, so the left-to-right layout is doing the work. Laski and Siegler (2014) then showed the counting rule matters as much as the board: counting on from where the token is produced roughly double the gains of counting from one. This is the 0–100 version of that, and the column alignment adds the base-ten reading the ten-square board cannot show — the squares directly above each other share a ones digit, so crossing a row is what adding ten looks like. Expectations belong at the pooled meta-analytic g = 0.21 (Nelson 2025), not the original d.

The underlying idea: A hundred board is two structures at once: a linear count, and a base-ten grid in which moving up a row adds ten.
Where this sits in Illustrative Mathematics: 1st grade Unit 4: Numbers to 99 · 1st grade Unit 5: Adding Within 100
Sources: Siegler et al. (2009) · Laski et al. (2014) · Institute of Education Sciences / What Works Clearinghouse (2021) · Schneider et al. (2018) · Illustrative Mathematics / Kendall Hunt (2024) all references →

Related measured skills: MagPI · Number line estimation, ALPACA · Early operations. What this means