Teaching is part of a System (Part 2): Knowledge of Variation
In Part 1, I introduced Deming's System of Profound Knowledge (SOPK), specifically the aspect of appreciating the system as applied in a teaching context. Today, understanding variation.
I am not a teacher, at least in the traditional sense. I do teach as part of my leadership role. I am married to a teacher. Here, my experience is as a trained Improvement Advisor, underpinned by Deming's SOPK.
As part of my training, I studied Deming as applied to education (I like to learn from a variety of fields), influence David Langford, an acolyte of Dr. Deming, and more recently, John Dues, who also published his experience applying Deming's SOPK in education.
Variation is the norm
Every process in a system has variation. Nothing stays exactly the same. Deming taught us that there is the normal variation (‘common cause‘) and variation due to unusual circumstances (‘special cause'). This itself comes from his interpreting and refining the terminology of Dr Walter Shewhart,
Through Deming's vast experience training and consulting across many industries, his greatest take-away remains that 94% of variation in a system is common cause, inherent to the system itself.
Only 6% or so is due to special cause. Unfortunately, most of us have tended to explain variations as special cause, and overreact.
Teaching variations
What does this mean in teaching?
For most students, their achievement is within the range of ‘common cause‘. There will be a few ‘special causes‘ above or below, but for the majority, any differences are common cause, down to the system. Without making changes to the system, the achievements will vary as common cause variation. Ranking becomes meaningless.
Imagine we take a maths test. We might score 47 out 50, another time 48. Have we improved? Perhaps the next time we score 46, have we worsened? Using so few data points is dangerous, but so is assuming changes between tests are significant when they remain within the bounds of common cause.
This applies equally to performance management in any context. In most cases, performance is due to the underlying system, rather than individuals.
Related articles
Introduction to short series on Teaching through the lens of System of Profound Knowledge - click here
Teaching is part of a System (Part 1): Appreciation of the system - click here
Teaching is part of a System (Part 3): Theory of knowledge - click here
Teaching is part of a System (Part 4): Psychology - click here
Deming Network
Join our Deming Network hosted by the Chartered Quality Institute - click here.
Check out the LinkedIn Group for the CQI Deming Network and the YouTube channel.
References
Arthur J. Signals vs Noise – Special vs Common Cause Variation. QI Macros Lean Six Sigma Articles. KnowWare International Inc; 2015 [cited 2025 Nov 24]. Available from: https://www.qimacros.com/lean-six-sigma-articles/signals-vs-noise/
Deming WE. Out of the Crisis. Cambridge, MA: MIT Press; 1986.
Shewhart WA. Economic Control of Quality of Manufactured Product. New York: Van Nostrand; 1931.
