September 27, 2018
by Kerry McKee

Lesson plan

Mystery Numbers

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Students will be able to order numbers from zero to 20, and describe the relationship between numbers using content-specific vocabulary.

(10 minutes)
  • Randomly pass out a card with a different number starting with zero to each student in the class.
  • Tell students that when you say, "Go," students should line up in numerical order.
  • Have students look at the number on their card. Tell students to think about what numbers come before or after their number. Ask them to think about which other numbers they will be between.
  • Say, "Go!" and allow students time to line up in order.
  • Once everyone has lined up in order, have each student call out and hold up their number, beginning at zero.
  • Frontload vocabulary by asking students to notice which students are before and after them in the line. Ask students which other students they are standing betweeen. Point out that no one is before zero.
  • Collect the number cards and have students return to their spots on the rug.
(5 minutes)
  • Display a number line and comment on how students lined up in the same order that the numbers appear on the number line.
  • Tell students that today they will practice guessing a mystery number that is between two other numbers.
  • Review key vocabulary by asking students which number is between 10 and eight. Have students show you the number nine on their fingers. Repeat with a few more examples. Have students repeat the word between after you, gesturing to point to their middle with two fingers.
  • Review the vocabulary word before by asking students to show you on their fingers which number comes before 10.
  • Have students repeat the word before while pointing in front of themselves.
  • Review the vocabulary word after by asking students what number comes after six. Have students repeat the word after while pointing behind their backs.
(5 minutes)
  • Display a number line with numbers zero to 20 or greater.
  • Show students two sticky notes with stars drawn on them, and tell them that today they will play a game called Guess My Number.
  • Begin by placing one sticky note on zero, and the other on 10. Tell students, "My mystery number is between zero and 10." Call on student volunteers to guess the mystery number.
  • As students guess, reinforce key vocabulary. Say something like, "Good guess! Six is between zero and 10, but my number is before six." Move one of the sticky notes to six and say, "My number is between zero and six."
  • Continue moving the sticky notes as students guess until they guess your number.
  • Play a few more times, and include the teen numbers up to twenty.
(10 minutes)
  • Pass out individual whiteboards, or white paper inside a sheet protector, and dry erase markers to students.
  • Tell students you will provide clues, and students should write the mystery number on their whiteboards.
  • Say, "The mystery number is between 12 and 14." Students should write 13 and show you their whiteboards.
  • Say, "The mystery number is just after nine." Students should write 10, and show you their whiteboards.
  • Say, "The mystery number is just before 12." Students should write 11, and show you their whiteboards.
  • As students demonstrate mastery, choose a student volunteer to call out a clue, or have students play in partners.


  • Provide a student number line and two sticky tabs per pair of students. Have students play Guess My Number in pairs.


  • Tape a number line on students' desks for reference.
  • Have students build number quantities with math counting manipulatives. Show them that a number that comes right after another number is one more, and that a number that comes right before another number is one less.
(5 minutes)
  • Check that students are able to identify numbers that appear between two other numbers on the number line during the Guess My Number activity.
  • Use the whiteboard activity as a formative assessment to assess students' understanding of key vocabulary words: before, after, and between.
(5 minutes)
  • Review with students that the numbers between 10 and 20 are called the teen numbers.
  • Send a number line zero to 20 and two sticky tabs home with students. Remind them of the steps to play Guess My Number: think of a number, tell your partner what numbers the mystery number is between, and move the sticky tabs as your partner guesses. Tell them to play Guess My Number with someone at home.

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