How many of us have been at the start of a PBL unit, right after introducing the driving question—designed to explore a complex problem—when a student confidently asserts something like, "Pollution? It’s all because of cars!" This reflects the surface-level understanding common at a project’s start, given that deep inquiry hasn’t begun.
PBL offers a valuable opportunity for students to move beyond their initial perceptions, engage in deep inquiry, and develop a more nuanced understanding of complex problems. One of the things I always loved about PBL was witnessing how students' thinking evolved as they learned. To capture this transformation and document their discoveries, I used an exercise in my classroom for years: The Problem Tree. This visual and interactive tool helps students analyze the root causes and effects of a problem, revealing the complexity and interconnected nature of the issues they are investigating.
What Is the Problem Tree Exercise?
The Problem Tree is an exercise defined in Design Thinking: Process and Methods (5th Edition) by Robert Curedale that provides an overview of all the known causes and effects of an identified problem. It shows a structured hierarchy of problems, with higher-level problems branching into related groups of sub-problems. By using the Problem Tree, students move beyond initial assumptions to uncover the layers of factors contributing to the problem, fostering deeper understanding and meaningful inquiry. I always used this exercise once students had gathered information and deepened their comprehension of a topic. Later in this blog, I’ll elaborate on why timing matters.
- The trunk: Represents the central problem.
- The roots: Show underlying causes.
- The branches: Highlight effects and consequences.
For example, in a unit on pollution, the trunk might represent “local pollution.” The roots explore causes like industrial runoff or inadequate recycling. Meanwhile, the branches show effects such as harm to wildlife, impact on people’s health, and lower water quality. This visualization helps students see how various factors interact.
The Problem Tree fosters:
- Systems Thinking: Understanding how causes and effects interact within a broader system.
- Deeper Inquiry: Asking “why” repeatedly to uncover core issues.
- Collaboration: By engaging in group discussions and incorporating diverse perspectives, students synthesize multiple ideas and viewpoints, which leads to more creative, well-rounded solutions once they get to this part of the project.
This exercise also reflects the core of cognitive demand, one of our equity levers. By holding high expectations for every learner and providing the right support, we ensure all students can engage in meaningful, rigorous intellectual work. As Zaretta Hammond highlights, building “learning partnerships” helps students persist through challenges, grow in confidence, and strengthen their academic mindset.
Using the Problem Tree Across Grades and Levels
While I primarily used this exercise with upper elementary students, younger learners can also engage meaningfully with appropriate scaffolding. For younger students, instead of having each student create their Problem Tree, you can facilitate it as a whole-class activity. This approach allows everyone to contribute collectively. Additionally, they can use drawings or symbols to document their ideas, providing a developmentally appropriate alternative to written responses.
Why Timing Matters
Introducing the Problem Tree at the right moment is key. Ideally, it should follow foundational research about the issue. This ensures students’ analysis is based on evidence, not assumptions. If introduced too early, students may populate the tree with ideas rooted in biases or misconceptions, as they won't yet have the research or data to support their thinking. While this can still spark valuable conversations, doing the Problem Tree midway through the PBL unit makes it an evidence-based analysis and encourages iteration as their understanding deepens through further investigation.
For instance, in a project I conducted on a bus driver shortage, students first gathered data, read news articles, and interviewed a bus driver to gain a deeper understanding of the issue. Through their research, they explored how the pandemic exacerbated the problem, with factors such as health risks, increased workloads, and early retirements contributing to the shortage. Equipped with this knowledge, they identified root causes like low wages and long hours, and mapped effects such as transportation delays and family stress. This preparation not only deepened their inquiry but also led to proposed solutions that centered on multiple needs.
Here are some tips for integrating the Problem Tree into your practice:
Start After Research: Ensure students have enough background knowledge.- Encourage Collaboration: Work in pairs or small groups to enrich analysis.
- Provide Materials: Use sticky notes, chart paper, or digital tools for flexibility. (I've always had students do this on large 11x17 or poster paper, giving them ample space.)
- Facilitate Reflection: Guide students to reflect on how their analysis informs solutions.
Avoiding Oversimplification and Growing Essential Success Skills
I’ve seen this firsthand: over time, students develop a mindset rooted in understanding complexity and recognizing the many factors shaping any issue. This process sharpens their curiosity, guiding them to ask deeper questions, seek meaningful answers, and connect causes to effects. The Problem Tree supports them throughout different phases of the project, most especially when generating new questions. It provides specific topics to explore further. Additionally, when students propose solutions, the Problem Tree is a guide for them to reference and design solutions that address complexity rather than oversimplifying it. Like a tree’s roots anchoring its trunk and branches spreading outward, this approach equips students to explore real-world challenges with a holistic perspective.
Try it out and tell us how it goes!
If you try this exercise in your next PBL unit, we’d love to hear about it! Please share your experiences with us. Also, if you want to explore more exercises like this one, check out Design Thinking: Process and Methods (5th Edition) by Robert Curedale for additional tools and strategies to enhance your PBL practice.
