Billion Oyster Project

Measures of Central Tendency


Oysters & Organisms Lessons



Class Periods




Subject Areas



Students start with a simulation of measuring spat-on-shell. They then find the central tendency measurements of their simulation. After that, students examine data from the Governor’s Island oyster docks. Students compare a set of discrete data (number of spat-on-shell) with a set of data that is continuous (length of oysters). They discuss which measure of central tendency: mean, median, or mode, is useful in which situation and why.


  • Find mean, median, and mode.

  • Decide which measure of central tendency is most useful in different situations

Materials and Resources


  • Oyster spat-on-shell simulation.
  • Real oyster shells with a bunch of spat-on-shell on each one, or if you can’t get those, drawings of oysters with a number indicating how many spat on shell are on them.
  • Drawings of oysters with numbers on them.
  • Calculators

Before you get started

Tips for Teachers

Try to make the simulation at the beginning as fun and engaging as possible. It would be best to pretend to pull a “cage” (box) out of the water and then count the oysters. You could even wear gloves! One option for the simulation is to set up your own classroom oyster tank and use the spat-on-shell from the tank. See the lesson entitled “Oyster Tank Setup (Part I What’s in our tank?) Any data set can be used for the second activity. Just make sure that the data you use has a mean, median, and mode that can be calculated.


On Governor’s Island several years ago, oysters were grown in bays in the dock, known as FLUPSY buckets (FLoating UPweller SYstem). The oysters were grown in the harbor and were an experiment to see how oysters survived living in and eating out of harbor water. The data for this lesson looks at the oysters grown in that system and analyzes the data using measures of central tendency.

Instruction Plan


  1. Teacher has a box of pretend oysters (or real shells with numbers written on them), each has a number on it to indicate the number of spat-on-shell  on each one. 7 students volunteer to come to the front of the room. Each picks an “oyster” from the bag, then records the number of spat on shell on each one. Teacher puts all seven numbers on the board.

  2. Example numbers: 4, 10, 5, 7, 7, 6, 0

  3. Teacher introduces the mean, median, and mode and then the students find all three using the Data Warmup.

  4. Teacher leads discussion around the following topics:

  • Mean: Can you have a partial oyster spat? Does this number still have meaning? Why or why not? Are there any outliers that are dramatically throwing off your results?

  • Mode: There are too few numbers for the mode to matter.Is there a discussion question here?

  • Median: This is probably the most useful in this case. Why?


Students are given the data worksheet. They put the data in order, then they find the mean, median, and mode of both sets of data.


Students complete the analysis questions and discuss.


Students look at Protocol 2 -Oyster Measurements in the Oyster Restoration Station Field Manual and discuss which central tendency measurements they might use with Protocol 2. 


CCLS - ELA Science & Technical Subjects

    • Integrate information presented in different media or formats (e.g., visually, quantitatively) as well as in words to develop a coherent understanding of a topic or issue.

CCLS - Mathematics

    • Understand that a set of data collected to answer a statistical question has a distribution which can be described by its center, spread, and overall shape.

NGSS - Cross-Cutting Concepts

  • Patterns

    • Patterns in rates of change and other numerical relationships can provide information about natural systems.

NGSS - Science and Engineering Practices

  • Analyzing and Interpreting Data

    • Analyze displays of data to identify linear and nonlinear relationships.