Iterative Phase

With time often being the main culprit, the iterative step in the engineering design process is typically underused and frequently skipped in STEM lessons. However, a real world engineering design process project should ensure that iterations are a crucial part of the practice. And an effective STEM lesson should have the following elements to nurture an iterative experience for learners. 

  • Criteria-based problem statement
  • Testing mechanism and process
  • Evaluation metrics tied to performance indicators
  • Time for improvement
  • Culture that supports and encourages failure

“Great design is iteration of good design” - Cobanli

Criteria-based Problem Statement

The design challenge prompt sets the stage for the iterative phase and a problem statement lacking strong criteria for the project will present issues later in the engineering design process. A well thought out challenge will force learners to empathize with the problem statement and establish design constraints to build their solution. Design facilitators may or may not reveal these design constraints during the first phase, but a strong design challenge prompt will allow learners to think critically about what they are building. For example, if you are facilitating a bridge design challenge, it is important to go beyond one criteria such as which bridge can hold the most weight. In the real world, engineers are not designing a bridge to hold the most weight, but rather a minimum load capacity amongst other critical variables. A strong problem statement should challenge learners to design based on multiple variables like the following: weight, height, length, minimum load capacity, budget of materials, lateral load and/or aesthetics. And when you are designing with multiple variables in mind, it will be imperative that iterations will play an important role in addressing the needs. 

Testing Mechanism and Process

A strong engineering design challenge will provide learners an opportunity to authentically test their ideas and solutions with a testing protocol. The testing protocol should be transparent for the learners and have a process to measure the outcome of a design. Finding tools to measure outcomes of a project will be important in gathering data on the success of project designs. Here are some example tools we recommend having in your toolbox when testing the different engineering projects out there. What other measurement tools do you use in your engineering projects?

Testing Mechanism

Measurable Outcomes

Tape Measure

Length, Width, Height, Distance



Luggage Scale

Load Capacity, Weight 

Digital Force Meter

Compression and Tension


Vibration, Motion of a Structure


Voltage, Current, Resistance


Thickness, Outside, Inside, Depth, Step Measurements






Vertical and Horizontal Accuracy 


Radius, Diameter, Distance

Pressure Gauge

Force applied by the fluid on a surface

“You can't improve what you don't measure.” - Peter Drucker

Evaluation Metrics Tied to Performance Indicators

Gathering data from measurement tools will naturally feed into evaluation metrics to determine the outcomes of many design challenges. For facilitators, it will be important to determine what performance indicators are valuable in evaluating the success of a project. And once you determine those priorities, having a performance index will be a valuable tool in assessing progress of prototypes. In its broadest definition, a performance index is a calculation of how well work is meeting its defined goal. Using the bridge design challenge example, a performance index can calculate the outputs from variables like weight of bridge, load capacity and length of bridge to determine how successful the project addresses the problem statement. Moreover, if the facilitator wants to highlight the budget of materials used in the bridge over another metric, the performance index calculation will put emphasis on that indicator. Typically that would mean the formula or algorithm will have higher exponential worth over a metric like load capacity. Here is a link to the UCSD COSMOS program that provides an example of a performance index on a CORI project. 

Time for Improvement

This section speaks for itself and is often the main roadblock to facilitating the iterative step during design challenges. If we are to provide real world engineering experiences, giving learners ample time to work on their design projects is absolutely necessary. In order to do that, teachers competing for time in their curriculum will have to balance quality over quantity. Are we facilitating engineering experiences for the novelty of play, exploration and tinkering? All which have value in their own right. Or are we focusing on giving students a real world experience by diving deeper with the engineering design process? And if the goal is to dive deeper, then we need to provide the time and space for improving initial designs and valuing a culture of iteration. 

“A person who never made a mistake, never made anything new” - Einstein

Culture that Supports and Encourages Failure

Our traditional education system relies heavily on Pass or No Pass, A’s or F’s, and Satisfactory or Unsatisfactory vernacular, which leaves many disfranchised and doesn’t provide authentic feedback in learning. When a learner doesn’t have an opportunity to improve on a test they failed, then we are not providing a real world experience. If that were the case in the engineering industry, there would be no innovation. Ask any engineer, their first attempt in testing a solution usually results in failure. But we don’t just stop and accept the failure, engineers embrace the failure and work on making it better. In fact, the failure reveals the insight to improve their designs. The culture in engineering is to learn from mistakes and support each other to refine their ideas. This is the culture we want to embrace in education and encourage our learners and facilitators to nurture. 

When these guiding principles drive your lesson plan, the engineering experience will feel more real world than ever before. While the ideation and creation phase of the engineering design process tends to get all the attention, the iteration phase is where innovation truly manifests and key life skills are developed. This is where engineering focuses on the problem it needs to truly address and instills a culture that the solution can always be better. 

“Few ideas work on the first try, iteration is the key to innovation” - Thrun