Invasive Species Council of British Columbia

Stop the Spread Freeze Tag

Grade: 4 to 7

Duration: 45mins - 1.5 hours

Setting: Indoor/outdoor

Subjects: Math, Science

Physical Activity: Yes

In this active game of tag, students learn the importance of early detection and rapid response to stop the spread of invasive species. Explore how the spread of invasive species can be affected by different variables including exposure time, the number of invasive species introduced, and early detection. Students make hypotheses and data is collected while playing the game outdoors. Details are included on how students can analyze results from the game back in class.

This activity is part of the Lesson “The Invasive Big League and the Away Team Advantage”, where students engage in discussion, analysis, investigations, and interactive indoor and outdoor games to discover the adaptations that give invasive species a competitive edge. Students also explore ways that people may help correct the imbalance posed by invasive species and “help our home team”.

Related activities
Inquiry Questions
  • What are the impacts of invasive species and what can I do to help lessen them?
  • How does early detection and rapid response affect the spread of invasive species?
  • What could happen if no one takes action to prevent the spread of invasive species?
BC Curriculum Links

Science Big Ideas

  • All living things sense and respond to their environment (Grade 4)
  • Multicellular organisms have organ systems that enable them to survive and interact within their environment (Grade 5)
  • Multicellular organisms rely on internal systems to survive, reproduce, and interact with their environment (Grade 6)
  • Evolution by natural selection provides an explanation for the diversity and survival of living things (Grade 7)

Science Curricular Competencies (Grades 4-7)

  • Demonstrate curiosity about a scientific topic or problem of personal interest
  • Explore and pose questions that lead to investigations
  • Evaluate whether their investigation methods were fair tests
  • Transfer and apply learning to new situations
  • Communicate ideas and findings in a variety of ways

Math Big Ideas

  • Patterns expressed and identified in tools and tables (Grades 4, 5)
  • Linear relations (Grades 6, 7)


  • 2 colours of pinnies or arm-bands
  • cones or playing area boundary markers
  • stopwatch
  • 1 clipboard and pencil
Documents to Download
  • Stop the Spread! Game Set Up and Datasheet
  • Stop the Spread! The Invasion Curve

Invasive species have adaptations that help them to spread and take over, causing environmental damages and having economic impacts. (For general information on invasive species and their impacts, read Background on Invasive Species for Educators. If invasive species are discovered and reported early, a coordinated effort can be launched to control or eradicate them, minimizing their spread and negative impacts and greatly reducing the financial costs of control. This is called Early Detection and Rapid Response (EDRR), which is a preventative approach to managing new outbreaks of invasive species. EDRR aims to find, identify, and address invasive species before they become widely established and cause harm to the natural environment, the economy, or public health.

The Invasion Curve (available in Documents to Download section, above) depicts the spread of invasive species over time and the cost of that spread. The longer an infestation goes untreated, the greater the costs – both to the environment and monetarily. In addition, the number of individuals in an area can have an effect on the area it is introduced to. A larger population of invasive species results in a higher impact on the environment compared to a smaller population of invasive species.

We can learn how to identify and report invasive species to reduce these ecological and economic impacts at   


It’s useful to have done some introductory activities and learning about invasive species and their impacts before playing this game.

  1. Make a copy of the Stop the Spread- Game Set up and Datasheet; get a clipboard, pencil, and timer.
  2. Set boundaries in a large playing field.
  3. Describe the game to students. Emphasize that blocking and pushing are not allowed and remind them that several rounds will be played.
  4. Assign roles to students and hand out coloured identifiers.
  5. Download a copy of Stop the Spread- The Invasion Curve for discussion and analysis in the classroom after the game.

Game Overview 

This is a freeze tag game where Invasive Species tag Native Species. In each round of the game a different variable is changed. Only one variable is changed per round so that students can predict and analyze the effects of that particular variable. The teacher or another adult will be timekeeper and record data for each round. Students will analyze the data after the game, back in class.

Stop the Spread Freeze Tag is based on The Stewardship Tag Game, in “Aquatic Invasions! A Menace to the West”, Oregon Sea Grant, Oregon State University.

Game Description and Roles

At the beginning of each round, students are assigned a role. Explain to students what each role can do.

  • Native Species – (Identified by coloured armband or pinnie). These students need to avoid the Invasive species. If they are tagged, they freeze and slowly count out loud to 10 (1 cat and dog…2 cat and dog…; or make it fun and say the name of your region- with a multi-syllabic name- after the number, e.g. 1 Okanagan or Vancouver Island or Lower Mainland, etc). Native Species can be “freed” by getting tagged by a First Detector within 10 seconds. If they are not freed by the First Detector, they remove their arm band/pinnie and become an Invasive Species. Even in rounds where there are no First Detectors, tagged Native Species should freeze and count to 10 before becoming an Invasive Species. Any Native Species that is frozen/still counting at the end of a round is considered an Invasive Species for the purposes of data recording.
  • Invasive Species – The Invasive Species will try to tag players who are Native species. Remember: No blocking or pushing.  No contact adaptation:  instead of tagging, Invasive Species could use long pieces of flagging tape or pool noodles, representing their seeds that shoot out and colonize an area.
  • First Detector – (Identified by a different coloured arm band or pinnie). First Detectors unfreeze Native Species by tagging them before they finish counting to 10. First Detectors are not tagged by Invasive Species. No contact adaptation: instead of tagging, First Detectors could get within arm’s reach and call out the name of that student/the Native Species, to signify that they have been “identified and reported”.
  • Explain to students that this game is a way to model how different factors (variables) impact the effect of invasive species on native species. Each round will change one variable so that we can predict the effect of that change. Tell them that you will be asking for their hypothesis and recording data for each round, and that there will be time for discussion and analysis of the data after the game.
  • At the beginning of each round, explain the scenario to your students and have them hypothesize the outcome of that round. Record the parameters (time, # of Invasive Species, # of Native Species at start and end) and the class hypothesis on the datasheet.
  • At the end of each round, count the remaining number of Native Species and record it on the datasheet. Compare the results of each round to Round 1 to see how the different variables change the impacts of the Invasive Species.
  • Play the game!  See the variables and timing for each round in the table, below, and the details on the questions to ask and review discussions after the table.

Game Procedure

The following chart and description are also available on the Stop the Spread! Freeze Tag Game Set Up and Datasheet.

 Round 1Round 2Round 3Round 4
Time30 seconds15 seconds3030
# Invasive Species2-3Same as Round 1 (2-3)Double Round 1 (4-6)Same as Round 1 (2-3)
# First Detectors0002
# Native SpeciesAll remaining studentsAll remaining studentsAll remaining studentsAll remaining students

Round 1: Long Exposure to Invasives, No First Detector

Baseline impacts when there is no intervention

Hypothesize- Ask the students: What do you predict will happen to the Native Species when the Invasive Species go undetected, and no one acts to stop them?

Expected Outcome: If nobody takes action to stop the Invasive Species then most, if not all, of the Native Species will be impacted (tagged) by Invasive Species.

Review- Was your hypothesis supported?  What were some things that could have slowed down the spread of the Invasive Species? (Remove some Invasive Species, give them less time to spread; introduce some competition or a predator)

Round 2:  Short Exposure to Invasive Species, No First Detector

Reducing the amount of time that invasive species have to spread.

Hypothesize- Ask the students:  What do you predict will happen to the Native Species when the amount of time the Invasive Species have to spread is decreased?

Expected Outcome:  If the Invasive Species have less time to spread, then fewer Native Species will be affected (tagged) by the Invasive Species compared to Round 1.

Review- Was your hypothesis supported?  Compared to Round 1, how did having less time change the impact of the Invasive Species? What situations in nature could reduce the amount of time that invasive species have to spread? (Early detection and reporting/ eradication efforts)

Round 3- More Invasive Species, No First Detector

Increasing the number of invasive species to start with. When invasive species go undetected and reproduce, their numbers quickly increase as do their negative impacts.

Hypothesize- Ask the students: What do you predict will happen to the Native Species when there are more Invasive Species to start with?

Expected Outcome-If there are more Invasive Species to start with, then most, if not all, of the Native Species will be affected (tagged) by the Invasive Species.

Review- Was your hypothesis supported? Compared to Round 1, how did starting with more Invasive Species impact the Native Species? If Round 1 and 3 both ended with no remaining Native Species, did this outcome occur more quickly in one of the rounds?

Round 4- First Detectors!

By reporting invasive species early, we can counteract their negative impacts.

Hypothesize- Ask the students:  What do you predict will happen to the number of Native Species if there are First Detectors who identify and report the Invasive Species?

Expected Outcome-If there are First Detectors working against the Invasive Species, then few Native Species will be turned into Invasive Species.

Review- Was your hypothesis supported? Compared to Round 1, how did adding First Detectors change the impact of the Invasive Species?

Discussion and Analysis

Back in class discuss what happened in each round of the game.

  • In which round were the Invasive Species most successful? Least successful? Do you think First Responders make a difference on the impact of invasive species in real life?
  • How does this game/simulation represent real life situations in nature? Consider some native and invasive species in your region.
  • What other questions do you have and how could we change the variables in the game to test your question?

Show the students the datasheet from the game. Have them work individually or in small groups to calculate the percent change in native species in each round and compare the changes. Which variables had the greatest and least effect on the impact on Native Species. Why?

Show the students the graph Stop the Spread Freeze Tag- The Invasion Curve and discuss it. Identify points on the curve and how they connect to each round in the game.  

Share with us!

We’d love to have your feedback and see photos of your students’ learning and participation in this activity. Send to for the opportunity to win resources and have your class have a virtual visit with an invasive species expert!

  • Learn how to be a real First Responder!  Have students learn how to use reporting tools such as Report Invasives BC (a free app or web-based form). Find an invasive species and submit a report.
  • Find out which invasive species are high priority for EDRR in your region and learn how to identify them so that you can report them if you see them.
  • Do some invasive species math!  Calculate and graph the growth rate of a population of an invasive species based on realistic assumptions. For example:
    • A female bullfrog lays 20,000 eggs but only 1% survive to become tadpoles, and 10% of the tadpoles survive to become adult bullfrogs. If a pond starts out with 10 female bullfrogs (and some male bullfrogs), how many eggs will there be in the pond that spring? How many will become tadpoles? After all the surviving tadpoles mature into frogs, how many bullfrogs will there be next year?  Assuming the same survivorship and an equal sex ratio (50/50 male/female), calculate the number of eggs, tadpoles and bullfrogs after 2 and 3 years. Graph the change in population over the 3 years.
    • Exponential growth of nutria in a wetland activity: Myocaster Multiplier, from Menace to the West, Oregon Sea Grant, Oregon State University.
    • Make up examples of your own based on invasive species in your region.
  • Discuss methods to control invasive species once they are established in an area, such as the introduction of bioagents (predators, parasites, or pathogens of the invasive species). A list of some invasive plants in BC and their bioagents is found here. how the game could be changed to incorporate a bioagent. Have students hypothesize how the introduction of a bioagent would change the number of Native Plants and/or Invasive Plants. Have the students brainstorm and come up with a plan on how to incorporate bioagents into the game, then try it out!