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One of my most vivid memories of childhood is carpooling with Brad’s mom to a church group when I was ten. It was early fall and we were talking about the changing seasons when she quoted her husband, an amateur astronomer: “We’re losing a minute of sunlight every day.”

That remark was so traumatizing that even now, almost twenty years later, I can recall the exact cross-street we passed when she said it.

I pictured neverending darkness. Riots. I wondered if we should maybe skip church group and stock up on flashlight batteries before the rest of town found out. Even at that age, my sense of patterns (and what a math teacher years later would call “indirect variation”) was developed enough to understand that we didn’t have much time left.

This is what I used to know:


That was a perfect, teachable moment for someone to step in and show me that what I used to know wasn’t good enough. “Not everything works like a line. Some things work like a cycle, getting bigger, getting smaller, getting bigger again. Can you think of anything else that works like a cycle?” Et cetera.

It has taken me six years to rewire my teaching to approach new knowledge as the solution to the limitations of what we used to know, rather than as an entry on a list of standards or “what we’re learning today.”


  1. The First Day Of Summer School.

11 Responses to “What I Used To Know Isn’t Good Enough”

  1. on 16 Sep 2009 at 9:16 pmMr. K.

    This vaguely reminds me of some of what I took away from reading Polya’s “How to Solve It” over the summer:

    Learning is not a process of acquiring absolute knowledge – it is a series of correcting subsequent misperceptions.

    It has made me much less panicked about making sure the kids get things right, and much more interested in how and why they get things wrong. That in turn allows me to more effectively move them forward.

  2. on 17 Sep 2009 at 1:39 amGraham Wegner

    After nearly 23 years of teaching, I still rewiring my approaches to work in the classroom. I like the phrase “in a constant state of re-invention”. What’s cool about blogs and the like is that I can use others (like your good self) to help figure out where to go to next.

  3. on 17 Sep 2009 at 7:19 amJulie Dirksen

    Lovely description of both flashbulb memory and the teachable moment.

    Reminded me of this:

  4. on 17 Sep 2009 at 8:04 amBert Bates

    Sorry that I can’t provide the proper attribution to this, but someone recently said that “efficient un-learning is the key skill in the 21st century”.

    Similarly, students of the game Go must unlearn previous tactics and strategies in order to progress. In many cases this unlearning is very explicit – “6 months ago I told you to play here – now that you’ve progressed you must forget that move and play in a new place”.

  5. on 17 Sep 2009 at 8:20 amJake

    It would be surprising to me if at age ten you were unaware of the cycle of the seasons. The days grow shorter in the fall and longer in the spring. It happens every year. How could you have missed it?

    I would venture to guess that you knew the seasonal cycle, and thought Brad’s mom was talking about something other than the normal seasonal change.

    Had your church group been studying the Book of Revelation, perchance?

  6. on 19 Sep 2009 at 7:44 pmChristian Long

    Beautifully said at the end of this post, Dan.

    Really dig this: “It has taken me six years to rewire my teaching to approach new knowledge as the solution to the limitations of what we used to know, rather than as an entry on a list of standards or “what we’re learning today.”

  7. on 20 Sep 2009 at 4:56 amKen

    I read this site all the time, but the nonsense your friend’s mother tells you is not knowledge you learned, it is a statement you did not know how to investigate. You were ten.

    You did not know this the same way you don’t know there really isn’t a “God”, as a child you just accept because children generally think their parents/adults know everything. As you get older, you learn how to determine what is knowledge and what is nonsense.


  8. […] What I Used To Know Isn’t Good Enough – dy/dan […]

  9. on 04 Nov 2009 at 8:20 ambubble

    Obligatory xkcd comic:

  10. […] in particular, my intention to be less helpful and my interest in a learning process that positions new knowledge as the solution to the limitations of old knowledge. As far as teacher mug slogans go, "create crisis" should start some good conversation in the […]

  11. […] BTW: Not for nothing, this is exactly how my mind worked. When I was ten. […]