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Teaching: Why A 'Mile Deep, Inch Wide' Approach Isn’t Always Best


There is a cliché saying in academia that tells teachers not to teach “a mile wide and an inch deep.” Wide and shallow is seen as an improper way to instruct students. However, that ‘mile deep, inch wide’ vision of teaching and learning does not accurately nor adequately address the challenges of teaching foundational material to students from diverse backgrounds with different skills and knowledge.

An inch wide and a mile deep is exactly what PhD candidates do in graduate school; they necessarily focus on circumscribed, bounded areas of study. Their topics are narrow so that they often know little about their field outside of their niche. And as these PhDs move forward in their careers, they are required to dig deeper and deeper into the same topic to gain and keep tenure.

As professors, they may know a lot about macroeconomics but little about what a person without a high school diploma must do to make ends meet. They might know about plant genetics but nothing about the politics and economics of genetically modified organisms (GMOs). Someone might know about how the drug war started and national drug policy but know nothing about the conditions for peasants in illicit drug producing countries whose only option for survival is to make or transport drugs. It is necessary for these Doctors to focus thusly, but it leads to limited, incomplete knowledge and can make a complete understanding of complex situations impossible.

Do we really want to create a bunch of ‘educated’ people that know nothing of the world outside their field of study? Unless they go to graduate school, isn’t it better to teach critical thinking, logic, and scientific methods and assist students to learn on their own, as deep or as shallow as they want? Isn’t a basic knowledge about how the world operates useful for all people? Wouldn’t it be great if every person in the U.S. knew about climate change, how elections work, economics, the history of slavery, and not just how to program an iPhone? How is going a mile deep going to help us with the important information we all need to be good global citizens?


If you have a hole, isn’t a mile wide and inch deep missing something, like a LENGTH! How long is this hole? Is the hole a square and thus a mile wide and a mile long? If it is a rectangle as suggested by the metaphor, then it has to be longer than a mile if the width is a mile. What if the hole is an inch wide, a mile deep, but 32 miles long? That would be quite a deep long hole. Why not a cube that is a mile on all edges? That would give us one cubic mile of knowledge.

There are some K-12 principals and managers of adult education programs who think we need to go deeper into fewer areas of study. However, high school is a time when students are studying a variety of topics; they will explore them more deeply in college. If they find subjects interesting and of value to them, students will explore them further on their own. Why limit the number of areas explored by going only “an inch wide?”

Certainly, we don’t want to just throw out minimal vocabulary and a couple of concepts in a given content and then expect students to learn what is necessary to develop and interest in those topics. That is why in high school there are various science classes, English topics and electives so students can explore various interests. What teachers and students must decide together is how deep and how wide they want to go and what would be the most useful strategy. First, you must give students information about areas you need to cover during a class based on standards and institutional requirements. Then you help them come up with a focus, areas of study and emphasis.

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If you are required to teach about the immune system, there are an infinite number of ways to go about it. Do you give a standard lesson with details about the immune system, discuss allergies, focus on infectious diseases or emphasize organ transplants? If you need to teach a lesson on the Bill of Rights you can emphasize the history of rights, focus on the First Amendment or talk about the Constitution in general. If you have time, why not all of the above? If you don’t have time, help the students develop the capacity to learn what they need on their own.

When we are young we collect knowledge through our senses using our nervous system, and like technological advances, we increase our knowledge based on what we know already. If we don’t come to class with a base of knowledge to build on, how are we going to learn the more advanced materials required of us? If a student doesn’t know what the U.S. Constitution is, how can we expect them to make sense of speeches comparing differing views on the elastic clause? How can we expect students to make sense of Kepler’s laws of planetary motion if they don’t understand Newton’s laws of motion? Unfortunately, adult education students don’t often come with a base of knowledge to develop a deep sense of any content area. They must start in the shallow end of the knowledge pool so they don’t drown in a mass of data.


Having the goal of creating thinking students is admirable, and it can be done with almost any topic. What we need to do is help students desire to learn and how to do it.

Societies want experts for work in fields such as cardiology, structural engineering, telescope optics design, and so on. However, there are few fields which require someone to have such a deep understanding of a narrow field. In fact, most jobs require you to have a wide variety of knowledge, and the more you know about related subjects, the better you will be at your job.

Nurses have to be generalists in order to help a wide variety of patients with wide-ranging ailments even if they later become specialists in pediatrics, for example. Mechanics need to understand the design of various models of cars and the computer systems to analyze them, and then later they can focus on a particular model of car. A police officer has to know about her weapons, how to communicate to the public, have evasive driving kills, know how to use computers and so forth.

The Center for the Collaborative Classroom believes that going a ‘mile deep’ is good idea, “…because of their complexity and thoughtfulness, we can’t just “cover” the national standards as we have with many of our state standards. At the conference, we were encouraged not to use words like alignment and covering when we reference the Common Core. Covering and alignment imply that our instruction is a mile wide and an inch deep. It’s NOT about covering any longer—what is important now is digging a mile deep and an inch wide into rigorous content.” Actually, you can study many of the standards without going a ‘mile deep’.

If your students can question, investigate, and explore topics, they will go as deep as required to meet any given standard. The job is in fostering curiosity or at the least helping students learn how to learn. Teaching the reading, writing and thinking skills that lead students to learn on their own is the real work, and that doesn’t require 'depth of knowledge.'

Without data, there is no wisdom.

Without data, there is no wisdom.

Certainly, a cursory take on subjects is not the best strategy, but neither is going a mile deep so one can’t cover enough topics to get a broad understanding of a field of study. We need to stop using this metaphor and teach as thoroughly and completely as the subject, level of class, and the students require. Unfortunately, this idea has become gospel because it is simpler to say, “mile deep, inch wide” than to look at overall curriculum, each class and level, individual students and lesson as a unique challenge with its own dimensions.

Tex Shelters

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