Filling in the teens

• CCSS-M · 1.NBT.B.3
  Compare two two-digit numbers based on meanings of the tens and ones digits, recording the results of comparisons with the symbols >, =, and <.

1.NBT.B.3 is about comparing numbers by size. Placing numbers on a line is comparing made visible: a child who puts 17 to the right of 12 is saying 17 is greater, and the line makes them commit to how much greater. This is order and magnitude, not proportion, which is exactly right for Grade 1.

This task runs unscored on purpose. At this age the line is a sequence, not a ruler, so treat it as a conversation about order and which side of the middle a number sits, not about exact distance.

1. Start: 0 at 8.3%
2. Drop 1: 20 at 91.7%
3. Drop 2: 10 at 50.0%

When to dropStart with only 0 showing and let the children place a couple of cards using just that. After two cards the Drop unlocks. Drop 20 first to fix the far end, and expect them to shuffle everything once it lands. Drop 10 next to give a middle to reason from.

Drop unlocks after 2 cards placed.

• 5

  at 29.2%
  Halfway between 0 and 10. A good early test of the idea of halfway.
• 12

  at 58.3%
  Just past 10, so just past the middle of the whole line.
• 17

  at 79.2%
  Close to 20, in the last stretch before the end.
• 8

  at 41.7%
  Nearly at 10 but not quite. Invites the question of which side of the middle it sits.

• Is this number closer to 0 or closer to 20? How do you know?
• Which of our numbers is the biggest? Where should the biggest one go?
• Is 8 before or after the middle?

• Looks like
  Numbers placed in an even row regardless of size, like beads on a string.
  Means
  Treating the line as a place to line numbers up in order, without attending to spacing.
  Respond with
  Ask whether the gap between 0 and 5 should look the same as the gap between 5 and 17. Let them feel that bigger jumps need more room.

There is no score here. Ask which number was the trickiest to place and why, and whether the 10 helped.

Numbers have an order and a rough position, and 10 is a useful landmark for deciding where a teen number lives.