Number Base Clocks

Shodor > Interactivate > Lessons > Number Base Clocks


The following discussions and activities are designed to deepen students' understanding of place value and base 10, as well as introduce them to other base values.


Upon completion of this lesson, students will:

  • have a deeper understanding of place value in base 10
  • understand how to convert from base 10 to other base values.
  • be able to perform simple addition and subtraction problems in base values other than 10.

Standards Addressed:

Student Prerequisites

  • Number Sense: Student must understand:
    • place value and what the different places represent
  • Arithmetic: Student must be able to:
    • Add and subtract multiple digit numbers in base 10
    • Use a basic algorithm to add and subtract

Teacher Preparation

  • Access to a browser
  • Pencil and paper
  • Base ten blocks

Key Terms

algorithmStep-by-step procedure by which an operation can be carried out

Lesson Outline

  1. Focus and Review

    Remind students what has been learned in previous lessons that will be pertinent to this lesson and/or have them begin to think about the words and ideas of this lesson:

    • Ask students to recall what they know about place value and base ten blocks.
    • Lead a discussion about place value to review basic terminology and understanding.
    • Ask students if they're familiar with the term "base ten".

  2. Objectives

    Let the students know what it is they will be doing and learning today. Say something like this:

    • Today, class, we will be talking more about place value and base ten and even learning about other base values.
    • We are going to use the computers to change numbers from base 10 to other base values, but please do not turn your computers on or go to this page until I ask you to. I want to show you a little about this activity first.

  3. Teacher Input

    • You may choose to lead the students in a short discussion about base ten.
    • Explain to the students how to do the assignment. You should model or demonstrate it for the students, especially if they are not familiar with how to use our computer applets.
    • Open your browser to Number Base Clocks in order to demonstrate this activity to the students.

  4. Guided Practice

    Try converting other numbers from base ten to other base values:

    • Have students convert from base ten to the other base using pencil and paper before checking their answers on the computer.
    • Lead a discussion on converting from base ten to address any misconceptions the students might have.
    • You may want to give the whole class certain numbers to convert into a specific base and check answers until they are ready to work on their own or in pairs.

  5. Independent Practice

    • Allow the students to work in groups of two to complete the Exploration Questions. Monitor the room for questions and be sure that the students are on the correct web site.

  6. Closure

    • You may wish to bring the class back together to discuss which base numbers were easiest to work with and why they think that is. Once the students have been allowed to share what they discovered, summarize once more the main points of the lesson.

Alternate Outline

This lesson can be rearranged in several ways if there is only one available computer:

  • Have students complete paper worksheets of problems with fractions on a number line and use Number Base Clocks to check some examples as a class.
  • Alternatively, select students who need additional practice to use the game. Teams of one strong student and one who needs help work well with this activity.

Suggested Follow-Up

This is an excellent lesson for understanding new base values and how to add and subtract in those base values. An excellent follow-up lesson is Clock Arithmetic

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