Stocks and Flows are the basic building blocks of system dynamics models. Using stocks and flows allows people to conceptualize both concrete and abstract concepts. A stock is an accumulation (trees in the forest, happiness of a child, water in the bathtub). A flow changes a stock over time. An inflow adds to the stock while an outflow subtracts with the stock. Like Behavior over Time Graphs, stocks and flows look at how a system changes over time, but they also represent interdependencies in a system.
Making Thinking Visible: Behavior over Time Graphs
A Behavior over Time Graph (or BoTG) is a simple line graph that shows a pattern of change over time – it shows how something increases and decreases as time passes. This foundational Systems Tool is instrumental in modeling and understanding many systems. By teaching how to create, use, and understand BoTGs teachers can help students understand concepts (simple and complex) in a more complete and robust way. The following five articles and curriculum provide a gateway to using this powerful tool in the classroom.
Three Things to Remember About Behavior-over-Time Graphs by Alan Ticotsky BOTGs are designed to represent our thinking. All BOTG graphs allow our 'mental models' to take a visual form so we can share them, or analyze them ourselves. Alan Ticotsky presents three insights which will help utilize BOTGs effectively.
Tuck Everlasting: System Dynamics, Literature, and Living Forever Carolyn Platt, Rob Quaden, & Debra Lyneis In this lesson, students use system dynamics tools to explore themes in the novel "Tuck Everlasting," by Natalie Babbitt. Students use behavior over time graphs and a simple system dynamics computer model to discuss their opinions on the story's major themes.
Building the Behind Closed Gates Model
By Anne LaVigne with support from the CLE and the Gordon Brown Fund
Behind Closed Gates: Power and Control
The Behind Closed Gates   simulation/model is loosely based on an experiment conducted at Stanford
University in 1971. The psychologist who designed that experiment, Phillip Zimbardo, wanted to see
how typical people would act if they were asked to take on roles of prisoners and guards.
The experiment and model are certainly about a prison environment, but they are also relevant to
many other similar scenarios. The experiment is frequently referenced when trying to understand
current and historic situations involving power and control.
Now you can build most of the underlying model and explore questions and situations beyond those
presented in the simulation.
Gail Falewicz has inherited the Critical Thinking and Reading (CTR) class from Mairéad Orpen. (See The Creative Learning Exchange, vol. 22, no. 1, Winter 2013.) As the CTR teacher, Gail teaches every 5th grade student at Innovation Academy Charter School (IACS), a public charter school, in Tyngsboro, MA. Here is her summary of the class structure and a report of a unit she taught based on the novel Among the Hidden by Margaret Peterson Haddix.
The purpose and scope of CTR can be summarized into three goal areas:
improve reading and comprehension skills
develop critical thinking and problem solving skills
promote the school’s four outcomes—Community Membership, Effective Communication, Problem Solving, and Self-Direction through whole class, small group and partner work
These goals are pursued through an academic curriculum that supports students across content areas.