K-12 Teaching and Learning From the UNC School of Education


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Learning outcomes

Students will:

  • learn the importance of washing hands in order to reduce or prevent the spread of germs
  • see mold grow on the potato that was handled by unwashed hands as compared to no or little mold growing on the potatoes that were handled by students with washed hands and hands cleaned with a hand sanitizer

Teacher planning

Time required for lesson

1 hour


  • three clean, dry potatoes
  • three glass jars with tight fitting lids
  • soap and water
  • individual paper towels
  • hand sanitizer such as Dial or Softsoap
  • warm place to store the jars
  • paper and crayons to draw and record the results at the end of each week


Students will need to know that germs will make you sick. They need to be aware that washing hands will kill germs or wash them away.


  1. Teacher divides the class into three equal groups. Each group is given a glass jar with a tight fitting lid. One group is the “clean hands” group. They label their jar “clean hands.” The next group labels their jar “dirty hands.” The last group labels their jar “hand sanitizer.”
  2. Allow each group to move about the room, touching desk tops, pencils, books, door knobs, pencil sharpener handle, any thing that a lot of students handle daily. They can also cough in their hands. Allow each group to move about the room, one group at a time, touching the SAME items. The “clean hands” group goes first.
  3. After they have moved around the room, collecting germs, they will wash their hands with soap and water and dry their hands with individual paper towels. Next they will line up facing the class and pass a clean potato from one person to the next, being sure to handle the potato well before passing it on to the next person. The last person in the line places the potato into the glass jar labeled, “clean hands,” and screws the lid on tightly.
  4. The “hand sanitizer” group will do the same as the “clean hands” group. Then they will clean their hands with the hand sanitizer, but they will allow their hands to air dry before handling the potato. They will also stand in a line facing the class, and pass a clean potato one to another, handling it well. The last person in the line will place this potato in the jar labeled, “hand sanitizer,” and screw the lid on tightly.
  5. The “dirty hands” group will follow the same procedure as the other groups. They DO NOT wash or clean their hands. They also stand in a line facing the front of the class and pass the third potato from one to the other, handling it well. Again the last person places the potato into the clean jar labeled, “dirty hands” and screws the lid on tightly. (The dirty hand group now washes their hands.)
  6. All three jars are placed in a warm location in the classroom. See Supplemental section for more information on mold.
  7. Teacher passes out art paper (12 × 18). Students label their paper “Growing Cooties” at the top. Students fold their paper to make four squares. Number each box from one to four, and write the date of each observation, as it occurs. Students will draw the potato experiment in the first box and label each potato. They should look the same.
  8. At the end of each week the students observe, draw, and label the potatoes as they change. At the end of the experiment, they will have a visual representation of the changes that took place. Continue the process for three weeks. The students should see mold growing on the “dirty hands” potato. This will give the students first-hand proof that washing hands does reduce or prevent the spread of germs.


Teacher observation of students’ drawings. Discuss results of experiment and why students think the dirty hands potato had more mold growing on it. Teacher observation of how well students wash their hands. Listen for comments students make about washing hands to see if they have internalized the lesson.

Supplemental information

Growth of germs will depend of warmth of jars. Germs could grow faster if your room is warmer. This may take less time than three weeks. Keep lids on at all times! At the end of the experiment, I throw everything away UNOPENED!

Mold is a plant (a fungus) and it uses water in its tissues. Unlike green plants, mold and other fungi don’t photosynthesize to make their food, but feed off of materials they land on. Molds don’t need sunlight, actually they grow as fast in the dark. They need only sunlight for spore production. In literature, it is recommended to grow mold in dark, moist, and warm place. The main reason for growing molds in the dark is that they might get dried out faster in sunny location. If you put your potatoes near a sunny window for warmth, let students know that mold doesn’t need sunlight to grow as other plants do.


This lesson was shared with me during my first year of teaching and has been around for a while. Children enjoy watching the gross changes that take place. The time frame for a good crop of mold will vary. I give it three weeks.

  • North Carolina Essential Standards
    • Healthful Living (2010)
      • Grade 1

        • 1.PCH.1 Apply measures for cleanliness and disease prevention. 1.PCH.1.1 Recognize that germs produce illness and can be spread from one person to another. 1.PCH.1.2 Use measures for preventing the spread of germs.

North Carolina curriculum alignment

Healthful Living Education (2006)

Grade 1

  • Goal 2: The learner will develop knowledge and skills to enhance personal and consumer health.
    • Objective 2.01: Describe and demonstrate measures for preventing the spread of germs.

Grade 2

  • Goal 2: The learner will develop knowledge and skills to enhance personal and consumer health.
    • Objective 2.02: Summarize methods for preventing the spread of germs through food, water, air, and touch.