Complicated is a descriptor of industrial age systems. The concept is built around a system-first perspective. Systems define people (think assembly line). Complicated systems have many moving parts, but are largely predictable, centralized, and codified. Because of this, the past largely predicts the future.
Complex describes dynamic and adaptive systems. The concept is built on a relationship-first perspective. People define systems, which means systems are alive and constantly changing. The past doesn’t necessarily predict the future and the outlier often has an outsized impact (think how one disruptive student impacts an entire class). Complex systems are frequently perceived as chaotic.
“Three properties determine the complexity of an environment. The first, multiplicity, refers to the number of potentially interacting elements. The second, interdependence, relates to how connected those elements are. The third, diversity, has to do with the degree of their heterogeneity. The greater the multiplicity, interdependence, and diversity, the greater the complexity.” 
In light of these properties, the abilities, lives, learning styles, and personal experiences of our young people and our families are infinitely complex. Layer those with the complex network of teachers, principals, administrators, and policymakers and I think the point is pretty clear. Education is complex.
And yet, we force-fit this complex human network into a highly structured and increasingly complicated, but still largely top-down, education system. We distinguish this type of school from that. This new pedagogy from the old. These types of students from those. The adults who support social/emotional wellbeing from those who do other things. In-school lives as students from out-of-school lives as youth. The school bus from the school hallway. Teachers from learners. You get the point.
But, it’s our young people who are forced to traverse this complexity even as we attempt to manage it as if it were complicated.
Our leadership and management models don’t match their realities. And, changing this is going to require deep commitment and time, but is an absolute necessity for an already changed world.
I suggest reading General Stanley McChrystal’s book Team of Teams to understand how he helped overhaul the entire premise and structure of national defense in response to the complexity of 21st century threats. Nothing on the planet was more complicated than the 20th century military industrial complex. But, for him, for the United States, changing from a complicated to a complex orientation was an existential imperative.
Perhaps when we own the same sense of urgency about education, we will have the courage to move beyond complicated systems designed for adults in order to do what’s right for the complex lives of our students.
It won’t be easy. Most adults won’t like it.
But, designing more complex education systems is the only way forward.
 “Learning to Live with Complexity” Harvard Business Review. September 2011.