Billion Oyster Project

Using Calipers to Measure Oyster Clumps


Oysters & Organisms Lessons



Class Periods




Subject Areas

Science, Math


Students will practice both identifying live versus dead oysters and measuring oyster spat in a series of competitive challenges.


  • Quickly identify live vs dead oysters.

  • Use a caliper to the tenth or hundredth of a centimeter.

  • Reflect on their work.

Materials and Resources


  • 10 oyster clumps (available from Billion Oyster Project) 
  • stopwatch 
  • poster-sized version of Live vs Dead Oyster Spat Time Trial 
  • calipers (at least 10, but the more you have available the better) 
  • index cards

Before you get started

Tips for Teachers

It is very helpful to have and extra adult or two (who knows how to use a caliper) in the room for this lesson. The best way for students to learn how to use a caliper is for them to practice and have someone check their work. Try to get some other teachers or volunteers into your room to help with this! You need to make sure all ten of your spat-on-shell substrate oysters are numbered (1-10) in some way. You must go through all ten substrate shells shortly before the lesson and count the number of live spat oysters on each substrate shell, so you know how to assess the students’ work. If the spat-on-shell are wet or muddy, plan accordingly. Leave time to rinse them off before class or provide paper towels to students so they are not distracted from their real work by the messiness.




Identifying live versus dead oyster spat

Dead oyster spat can be identified with a light tap on the top shell. If the shell is visibly gaping open, if there is softness or movement in the shell, or if bubbles are discharged when the shell is lightly pressed, this means the oyster is dead.

Dead oyster spat will also sound hollow when lightly tapped. To double check that an oyster is dead gently try to pry them open with your fingernail. A dead oyster will generally open very easily. Often a dead oyster is filled with mud and therefore can be mistaken for being alive. The ‘fingernail check’ is especially useful to make sure that the oyster is truly dead.

Instruction Plan


  1. In this activity, groups will race each other to see who can identify live oyster spat with the greatest speed and accuracy.

  2. Display a poster-sized version of Live vs Dead Oyster Spat Time Trial.  You need to be able to write on it.  

  3. Split the class into (ideally) 10 groups, so that you have one spat-on-shell for each group.  

  4. Hand out one copy of the ORS Field Science Manual to each group.  (You only need the section within Protocol 2 entitled “Identifying live versus dead oyster spat.”)

  5. Each group gets a spat-on-shell.  This is their practice shell.

  6. With this first shell, the students have as long as they need to identify the live vs dead oysters and count the number of live oyster.

  7. Circulate around the room, answer questions and point students to the directions in the ORS Field Manual. The teacher can help students identify the live vs. dead spat.

  8. Make sure all students are comfortable identifying the difference between live and dead oyster spat.  Then, record the students’ results of number of live oysters on the poster.

  9. Explain: Groups will do the same thing with the remaining nine spat-on-shell.  And at the end, we will see who did the fastest and most accurate work.

  10. The groups rotate their spat-on-shell, so every group has a new one. Do not let the students touch their new spat-on-shell yet!

  11. Now, get ready with the stopwatch.  

  12. When you say “Go!” the students in each group pick up their spat-on-shell and count the live vs dead oysters.

  13. As each group finishes, record their time on the poster.

  14. Once every group has finished with their spat on shell record their count of live oysters.  (Remember, you have counted all the live oysters before class, so you should know the correct answer for each shell.)

  15. Repeat this until all the spat-on-shell have been counted by each group.

  16. Declare a winner!  

  17. Ask: Do you think it’s important to work quickly when we count live oyster spat in the field?  Why or why not?  Look for good ideas about both possibilities, for instance -- yes, there are a lot of oysters to count and it’s good to work efficiently.  And yes, it’s important to collect accurate data, and to take the necessary time to do so,

  18. Solicit from students what other questions they are left with about oyster spat after completing this activity.  It’s important to keep track of these questions, ideally to post or share them with students on an ongoing basis.


  1. In this activity, the students learn or are reminded how to read a caliper.

  2. Each group gets a spat-on-shell.  This is their practice shell.

  3. Each group gets least one pair of calipers. The more calipers the better!

  4. Decide whether from here on out, how many decimals you want to the students to measure to.

  5. Project or hand out one or more of the caliper pictures in the Caliper Images powerpoint and review how to use a caliper.

  6. Circulate around the room to help students with their measurement practice.  (It is very helpful to have knowledgeable extra adults on hand for this portion of the lesson.)


  1. In this activity, students will practice measuring oyster spat in their groups.

  2. Each group gets one spat-on-shell.

  3. Each student gets a bunch of  index cards.

  4. Each member of the group take turns measuring the same oyster spat and writes the answer on one of the index cards.

  5. Everyone should “hide” their measurements and results from their group members for the moment.  

  6. After each member of the group take a s turn measuring the same oyster, the students count to three and reveal their measurements to each other.  

  7. If all group members have the same measurements they call you over to verify and they get a gold star/prize.

  8. If there is a discrepancy among their measurements, then the students take the time to measure the same oyster spat again, this time working together, to find the correct answer.

  9. Groups repeat this exercise with as many oyster spat as possible.


  1. Students write a paragraph or journal entry with a quick reflection on the lesson.

    1. What skills did you work on today?

    2. What questions about oyster spat are you left with?

    3. Do you have any questions or concerns about completing this protocol in the field?