Mystery Jars: Estimate Contents

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This activity puts a mathematical twist on the familiar “guessing jar.” No guesses allowed, estimates only. Choose an object that comes in two sizes, such as large and mini pompoms, and fill one of two identical jars with each. Ask learners to estimate how many in each jar and to write down their reasoning. Encourage them to read what each other has written and decide if they agree or not. If you must give prizes, give them out for good explanations of reasoning, but not for the closest answer. It’s estimation strategies that count. [Activity is publicly available through a web crawler capture on]

Quick Guide

Preparation Time:
Under 5 minutes

Learning Time:
5 to 10 minutes

Estimated Materials Cost:
1 cent - $1 per group of students

Age Range:
Ages 4 - 14

Resource Types:
Activity, Game


Materials List (per group of students)

  • two identical clear plastic jars
  • similar objects in two sizes for filling jars (small and large pasta shells, pompoms or beads)
  • recording sheets and pencils


  • Mathematics
    • Algebra
      • Patterns
    • Measurement
      • Size and Scale
    • Number and Operations
      • Multiples and Factors
      • Number Systems
      • Operations
    • Reasoning and Proof
    • Representation
  • The Nature of Science
    • The Scientific Process
      • Formulating Explanations
      • Communicating Results

Informal Categories

  • Games


To use this activity, learners need to:

  • see

Learning styles supported:

  • Involves teamwork and communication skills
  • Involves hands-on or lab activities


Access Rights:

  • Free access


Source Collection

  • Mixing in Math


  • , © 2010, TERC, Inc., MA., 2010

Funding Source:

  • NSF, ESI-0406675 and DRL-0713537