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Essential Science for Teachers: Physical Science

Density and Pressure Featured Classroom: Tina Grotzer; Arlington, MA

Tina Grotzer; Arlington, MA

“You can’t understand the nature of density without understanding matter. You can’t understand air pressure, and all of the weather-related phenomena around air pressure, without understanding matter. There’s just so much that builds upon it, I would call it one of the most fundamental and generative concepts that we can teach students.”


School at a Glance:
Thompson Elementary School
Arlington, MA

  • Grades: K-5
  • Enrollment: 323
  • Students per Teacher: 20
  • Ethnicity:
    76% White
    12% Asian
    7% African American
    5% Hispanic
  • Percentage of students receiving free or reduced-price lunch: 23% versus a state average of 29%

Nestled in the heart of East Arlington, Massachusetts, the Thompson School is one of seven elementary schools in the district that science specialist Nadine Solomon visits on a regular basis. In addition to working with the students and modeling lessons for teachers, she occasionally invites science education researchers like Tina Grotzer into classrooms.

Tina has had a long-term relationship with the Arlington Public Schools. She was a teacher in the system for many years, the coordinator of an elementary academic enrichment program, a teacher professional developer, and is now a researcher. As a researcher, Tina developed the Understandings of Consequences Project at Project Zero, at the Harvard Graduate School of Education. The Understandings of Consequences Project addresses the difficulties that students have in understanding cause and effect and how that influences their learning of scientific concepts. The curriculum that grew out of the project focuses particularly on the “non-obvious” causes of macroscopic phenomena, like rising and sinking, by making concepts like density more obvious.

Lesson and Curriculum

Causal Patterns in Density; Understandings of Consequence Project

Lesson at a Glance:
Curriculum: Understandings of Consequence Project, Project Zero, Harvard Graduate School of Education
Grade: Fifth
Topic: Causal Patterns in Density

Prior to this lesson, the students had been working with the Arlington science specialist Nadine Solomon and their teacher Nicole Scalzo in lessons on the nature of matter, states of matter, and what it means in terms of particles for something to be a solid, liquid, or gas.

In this lesson, by using brass and aluminum cylinders and controlling for two variables — mass and volume — Tina made the property of density more obvious to the students. She also began to address the causes for density differences in matter on the particle level, by asking the students to draw their own models for what they think the particles of the two materials would look like under what she called their “microscopic eyes.”

Tina commented, “One of the critical challenges in understanding density is that in addition to particle “crowdedness,” there’s differences between atoms, in terms of their mass. Eventually, the lessons that we’re doing today will lead into lessons on the nature of rising and sinking. What we’ll be trying to get the students to understand at that point is that it’s the relationship between the density of the object and the density of the liquid that accounts for whether it sinks or rises, not just the density of the object itself.”

Series Directory

Essential Science for Teachers: Physical Science


Produced by Harvard-Smithsonian Center for Astrophysics. 2004.
  • Closed Captioning
  • ISBN: 1-57680-749-5