I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. He / him. More here.


  1. I agree. I am not a math teacher. I am a Biology teacher. Nothing is more fun to see if they get it by having them reason out the size of a microscope field of view in high power if we know the field of view in low power (and all the magnifications). It can’t be seen so one has to rely on logic.

  2. Back in the day my mentor teacher did this activity with Blow Pops. Definitely a hit with the kids, and no talking while you debrief the activity. I wonder if he still does that activity…

    Most schools are No Candy Zones these days, so no one can use this idea.

  3. All right. So, what are the best ideas for teaching proportional reasoning? I think I do a good job, but magic? Not so sure. I don’t want to be sent to rehab without a fight.

  4. How does this “game” work? I’m wondering if I could adapt it to teaching the balancing of chemical equations to my students….

  5. This was the best activity I have ever done, period. I even got observed during one class and my administrator loved it.
    There’s a great video on unitedstreaming about how the capture/recapture method works that I played prior to the activity.

    Thanks Dan, I just discovered your blog and it’s nice to know someone is out there on the same plane. I even feel your pain on burning the midnight oil coming up with powerpoints (older post). It was totally worth it in year two, except the kids still didn’t care (for the most part). Although it did help with management a little, they just want to be entertained, not taught. Do you find a big impact on the atmosphere when you use those slides?

    Now I have moved to a different school that was supposedly more upscale and I don’t even have a classroom and they have hardly any technology to use!!

  6. Maybe I missed something, but what activity are we talking about? Did I miss a link, or is the goldfish picture an obvious reminder of a universally known proportions activity?

  7. I’ve done it by marking dried beans with a sharpie – nice activity…the colored goldfish crackers are a cute idea. Once they get it we play a little game called “How many kids in this school….” (have a dog, don’t have a lunch period, were born in another country, have divorced parents, etc etc) using the class as the sample representing the school – attendant discussions of how reliable those numbers are – big fun.

  8. Here’s my dilemma – I can’t think of one professional development/workshop/conference I’ve attended in the first 15 months of teaching that informs my curriculum even a shred as much as one post like this does…As a side note, I love this blog and the talent surrounding it. I bet that if this community could put together a conference, I might leave with some actual ideas for contextualizing algebra 2.

    How good does that sound – a conference of good, creative teachers…sharing ideas for curriculum and structures. I swear I’m too young to this profession to be such, but each hour I spend in “professional development” or working towards my credential when I know my time be better used to plan a good lesson makes me feel just a bit more jaded.

    Can anyone help on finding honestly beneficial ‘professional development’? I have a reasonable administration, but they can’t help me teach math…