Decomposition: Let’s Talk Trash

Photo by David Rosen, Wildside Photography

This great activity helps students become conscious of the things they throw away and what happens to them in the long term.  So grab a pair of gloves and prepare to talk trash with your students!


Bucket, gloves, newspapers, shovel or trowel for digging, scale for weighing

Advance Preparation

Arrange for the custodian to visit and help with answering questions. If you are providing a snack today, a banana is a good choice because the decomposing peel is fun to watch!


There are four parts to this activity:

  1. Collect and examine the school’s trash.
  2. Categorize trash by type and calculate volume.
  3. Place trash in buckets for decomposition.
  4. Create an action plan for your school.

Ask Questions

  • What do you think went into the cafeteria garbage today?
  • How about the trash in our own classroom?
  • Where do you think all of this garbage goes at the end of the day?
  • Who takes care of it once it leaves the classroom or the cafeteria?
  • Where does it end up?

Make Predictions

  • What does that trash look like in a week, a year, or a decade?
  • Is any of it recycled?
  • And what does it become if it is recycled?

Seek Answers

Arrange for the custodian to visit and participate today to answer questions:

  • What type of waste is discarded each day?
  • Is it paper, metal, plastic, milk cartons, food?
  • Does the school have a recycling program?
  • How could students reduce waste?

Encourage discussion and then put the gloves on and go dumpster diving!

Conduct Research

Students look for discarded material that went into the garbage today. Collect from several areas like the classroom, the office and even the playground. (There is bound to be some good garbage there). Don’t forget the cafeteria refuse. Ask the janitor to reserve some for you to examine.

Pour the items onto newspaper and separate into categories. If you have a scale available, weigh the items. Here is a chance to extend this into a math lesson. Calculate the average weight of garbage from three or four classrooms, multiply by 5 days in the week, times 4 weeks in a month, times the number of months in a school year, times the number of classrooms at your school. Do the same for the cafeteria waste. Boy, does it add up to a lot of trash!

Have students select items for their container. Ask students to predict how long it will take for each item to decompose. Students need to use a shovel to dig enough dirt to cover their trash and moisten the soil with enough water to dampen only. (No mud, please.) Put the lid on, poke holes in the top and place a label with their name and list of items on the side of the container. Next to their listed item, record a prediction of how many weeks it might take to decompose that item.

Draw Conclusions

Reach conclusions through discussion:

  • What items are most numerous in our school trash?
  • Why are they numerous? What can be done to reduce the amount?

Take Action

  • Consider what it means to: Reduce, Reuse, Recycle
  • Imagine ways to reduce, reuse and recycle and create a plan to do it at your school, your home, or playing sports.


Contact the County of Sacramento Waste Management for free materials.