EducationHigher Education

Active learning: does depth outweigh breadth?

The fox knows many things, but the hedgehog knows one big thing.  (attributed to the Greek poet Archilochus)

A friend recently sent me to a NY Times article on teaching science in the universities, whose lead-in point was, of course, how often it is done poorly.  The article went on to describe several innovative ways of moving away from the ‘lecture-only’ format to active learning.  By a number of metrics, these new methods have increased success in raising scores and increasing comprehension.

Yet, despite the documented successes, the article decries the resistance at most universities to changing their ways. The usual culprits are listed:

  • Professors don’t care about teaching.
  • Even if they care, teaching is irrelevant to career advancement.
  • Lecturing is easy, doing it in any other way is more work.
  • Professors like to weed out students, to limit access to more interesting advanced classes.
  • Universities just like to slavishly follow tradition.
  • You can’t tell a tenured professor to do anything!


In other words – all the usual tropes are dragged out.  In my experience all these are more false than true.  But that’s not my point in this posting.  When one speaks about active learning, it generally involves stopping your lecture to discuss a point more deeply.  Or having the class work out some relevant problem.  Or as in this article, having the professor run up and down the stairs, asking random students questions about the material.  What works here is that the lecturer gets immediate feedback as to whether or not the class is getting it.  And if they aren’t, then the lecturer can go over the material again (and again? and again?) until a satisfactory level of comprehension is obtained.

Obviously, if this is how the material is being taught, students will learn and comprehend it better.  However, whenever I read about active learning being extolled yet again, there is one cost that is never mentioned – time!  Every time you stop the class to actively learn about one topic, something else cannot be covered at all.  Consider the following.

I have taught Introductory Biology at UCLA.  We are on the quarter system (classes last 10 weeks), and I taught my class MWF for 50 minutes at a time.  This gives me exactly 25 hours total for when I have the students in front of me.  And actually less, given that I have to start a couple minutes late to let everyone find their seats, and end a couple minutes early so not to be drowned out by the masses departing early for their next class.  So, what can I cover in one ‘day’ of face time?

Certainly not all of Biology!  We’ve long ago recognized this and our course is better described as an introduction to evolution and ecology.  But even with this truncated definition of biology, here is a non-exhaustive list of subjects that could be covered in the class:

  • Mendelian genetics, plus the modern revolution in genomic biology.
  • Population genetics.
  • Evolution by natural selection.
  • Evolution by genetic drift and other stochastic processes.
  • The Tree of Life.
  • A march through the taxonomic groups of animals (which may be the only time many students would be exposed to the idea that there is more out there than mammals, birds, and fish).
  • A consideration of plants (again maybe the only class students will ever take that will let them know there is more in the world than trees, flowers, grass and ‘germs’).
  • Ecosystem ecology
  • Community ecology
  • Population ecology
  • Conservation biology.
  • Relevant modern-day problems for biology like climate change, biodiversity loss and disease outbreaks.
  • Infuse all of the above with an appreciation for quantitative methods: e.g., mathematical models and statistical analyses.


Can you get all this into 25 hours?  Maybe.  How about if you add in in-class active learning exercises for each topic, which doubles the amount of time you have to spend on said topic?  Now a lot has to come out – you just don’t have the time to even get to mentioning it.  And this is the tradeoff I never hear mentioned.

Now I could teach my version Intro Bio, by concentrating only on my one favorite topic: Natural selection.  After 25 hours of lectures, Q&A, think-pair-share, workgroups, clicker questions, and discussions you can be damn well assured that my students would walk out after the quarter comprehending natural selection very well indeed and scoring excellently on tests about it.  Success, right?  But have I really taught them an “Introduction to Biology”?

I will say that I do like much about active learning, and do try to incorporate it into what I do.  But I also know that it comes with this great tradeoff of depth for breadth.  In my advanced classes, which already have a more restricted focus, I am much more willing to go make this deal.  However, for at least introductory biology, I am not convinced that a better understanding of few things (via active learning) is worth the sacrifice of not being exposed to many things (via the classical lecture).  Do we want our students to become foxes or hedgehogs?

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Peter Nonacs

Peter Nonacs

Professor of behavioral and evolutionary ecology at UCLA. I study the evolution of social behavior and cooperation, and anything that ants may do. And occasionally people, too.


  1. December 27, 2014 at 2:08 pm —

    I often think that the way is to cull more and make sure students understand that well. With those basiscs they can the specialize. Also, make sure that content doesn’t double between different lectures.I swear there’s stuff I heard 4 times in 4 different lectures which were ALL mandatory, but of course never in depth. The second time it’s a refresher, the third time it 90 minutes of your life where your best shot is something interesting going on on Twitter.
    As for the usual complaints about lecturers: As a student in education I cannot understand how the highest level of education is handed to people who basically don’t understand shit about teaching. My university is now offering classes to lecturers, but they’re still voluntary (but constantly overbooked because people know that they have no clue about teaching apart from their experience as a student and want to improve. Sure, there may be a few fossils of all ages who don’t care, but most people want to be good at what they’re doing.)

  2. December 27, 2014 at 2:51 pm —

    You make a very good point; this is especially true for service courses. When I teach Calculus, there is material that must be covered, because students need to know it for their other courses (Physics and Engineering, in particular). Stop too long or spend too long getting the students to “discover the material for themselves” and you don’t cover the stuff that you need to cover and that others are depending on you to cover. In the end, most teaching techniques that I’ve heard or seen end up in the following: if you have a motivated, dedicated person spending all the time they need, then the students benefit. This is true of pretty much any method used (including lectures). And innovative teaching techniques are generally tried by the motivated and dedicated, so is it really that much of a surprise if they generally produce encouraging results? This was true of “work in groups”, “discovery”, “active participation”, etc. Why should it be any different with the newest techniques, “flipping the classroom”, “active learning”, etc. ?

  3. December 28, 2014 at 10:37 am —

    An interesting approach that was often taken by professors when I studied in Italy was to assign course readings covering the entirety of the required material and then limit class time to the exploration of a single topic in greater depth. Generally speaking the oral exams would mostly cover the special topic (50-75%) and then have a random smattering of questions about the rest of the stuff to make sure you learned it.

    Needless to say, it would make me very nervous to try anything like this in the North American system.

  4. December 30, 2014 at 9:43 am —

    Let’s not engage in this conversation without education research.

    “Eylon and Linn (1988) reviewed the literature in cognitive science and science education
    prior to 1988 in their quest to highlight strategies for improving science education.
    They cite more than 200 references in their synthesis of four major research perspectives
    used in science education: concept learning, developmental, differential, and problem solving.
    Viewed collectively, the authors concluded, “. . . in-depth coverage of several science
    topics will benefit students far more than fleeting coverage of numerous science topics”
    (p. 251). However, they also recognize that “few empirical studies demonstrate the efficacy
    of suggested methods” (p. 252).”

    The article goes on to show that high school biology students who experienced “no-depth” got no advantages in college courses, while those that experienced at least one topic in depth got significant advantages. “What these outcomes reveal is that although the choice to pursue depth of study has
    a significant and positive association with performance, the choice to pursue breadth of
    study appears to have implications as well. These appear to be that students whose teachers
    choose broad coverage of content, on the average, experience no benefit.” Additionally, they found that teachers who try to do both depth and breadth tend to lose the statistical improvements of depth-only classes, when viewed separately.

    Now, this is just the first paper I found on Google and it focuses on High School, but it seems legitimate and references at least a dozen other papers that agree with the same thing, which is also the conventional education research position: depth is vital over breadth. I view this choice as a choice between whether you want students to see a lot of stuff that they don’t learn, or learn some big ideas in a way that requires and improves critical thinking, metacognition (learning how to learn), and reduces negative collateral learning like “school is for learning lots of facts”, or “I just have to remember these things for school, but they don’t apply in real life”.

    The students you believe you are harming by not covering material (the ones that learn quickly and want to move off of a topic) will thrive in later classes regardless of concepts missed. Rather than speeding along to “cover” concepts, a teacher can use other techniques to differentiate learning, such as independent projects or encouraged extra-course readings or activities. This probably works a little better at the High School level where there is less pressure for everyone to be evaluated in exactly the same way. The research I have seen suggests that if you taught only Natural Selection, and taught it well, you’ll produce students who do phenomenally on Natural Selection, but do EQUALLY well on the content that they have never seen as compared to a breadth class that “covered it”. Covering a concept without taking time for students to understand it has essentially no benefit (and many negative effects).

    • December 30, 2014 at 1:24 pm —

      Your point is that it is more important to teach students how to learn than presenting any particular fact or set of facts (correct me, if I am missing the true point). I would go even further and say the critical thing students need to learn is how to think. And even at UCLA, a university full of over-achievers, it is troubling how often my students fear having to think. As boring and uninspiring as it might be, many will greatly prefer the safety of courses where they know all that is required is memorization and regurgitation. And to take your argument to its logical conclusion, one could say it is totally irrelevant what I chose to teach in ‘Intro Bio’ as long as I get the students to actively engage their minds with the material. Heck, it doesn’t even have to be biological! But here I must disagree. As important as it is to produce active learners and thinkers, it is as equally important to make them aware of the universe of things they could apply their newfound abilities to. When I get specific comments on my Intro course material, 90% of it is like, “I found X to be boring and useless for anything in my future. X should be dropped from the course.” However, about every 10th comment will be, “I never knew X existed. I plan to learn more about X in the future and may make it my career!” What is “X”? I don’t know – and I can’t predict it in advance for anyone. All I do know is that the broader the course is, the more chances I’ll have to connect someone to their “X”. Yes, too often breadth is facile and repetitive across courses. Too often breadth is equated with, “Here’s a set of facts about worms – learn them for the test.” But I am 100% in agreement with another of the comments above: It really is the teacher who makes the difference. In the perfect world, you’d have classes with teachers who know how to get you to think, and you’d also have classes with teachers who know how to show you the universe.

      • December 30, 2014 at 1:44 pm —

        Learning how to think and learn is certainly the most valuable skill that can be taught, but I wouldn’t say that an Intro to Bio class could present any material to the same effect. The teacher must decide what best drives her students to reach her goals. A deep and robust understanding of biology topics would be one of my goals in a biology class, but the breadth and depth must necessarily be limited (though I would argue that it’s not a true dichotomy). Teachers determine (sometimes with student input) what the big ideas of a subject are. My suggestion would be to think of “breadth” as a different beast: instead of trying to teach or lightly introduce topics to hit your curriculum goals, have activities to teach the big ideas that are deep, and then have activities that show breadth. The key difference here is that the goal of breadth activities shouldn’t be to teach the material – all taught material must have a goal of deep understanding. Instead, your activity’s goal is to introduce the “X” in your example, to pique student interest. Maybe your ‘breadth’ activity is a student driven research project where students investigate something that interests them from a list of topics. If your goal is to make students aware of the universe, the best way to do that isn’t usually to try to scratch the surface of understanding each thing, but to show the breadth and provide the tools to investigate them further.

        I admit that “teaching wide concepts” and “showing wide concepts” is a vague distinction: again, a teacher much go back to his goals for his students, and use these to inform his decisions. All teachers should be cautious about why they are doing what they are doing, and make sure their reasons are justified in the value to their students.

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