Teaching is hard.

There is a certain perception about teaching, held by many who have never taught. It is that teaching is like making a sandwich. If you want your sandwich to taste salty, you add some hard salami. If you want it to have some creamy tang, throw on a slice of sharp cheddar. A vinegary bite comes from some good brown mustard. Thinly sliced tomatoes give it a cool, wet crunch.

OK, now I have to go make a sandwich.

Now that I’m back (chew, chew, swallow, burp), I want to show why teaching isn’t like making a (bite, chew, mmmm, swallow) sandwich.

We have outcomes from teaching – goals, behaviors, walkaway messages, proficiencies, indicators – call them whatever you want. They amount to the same thing. If you teach this, they walk away with that. Mission accomplished. Pass the pastrami.

But learners aren’t cold cuts, or even really good cheese. Instead, learners wander all over the bread like some wildcard spice you’ve never heard of. Outcomes are inherently unpredictable. And that’s what makes them so amazing!

Here’s a story that shows how unpredictable outcomes are, and by the end it will (I think) explain my title. But you never know. Unpredictable.

In the early days of World War II, the British were under fierce attack by the German Luftwaffe. Radar installations along the English Channel provided some warning, but those early radar systems had a fatal flaw. The waves they produced were long waves, anywhere from a few meters to a hundred meters long.

The problem with long waves is that they wrap around their targets. Imagine trying to pick up a pea with a catcher’s mitt. Just as the catcher’s mitt can’t locate the pea very well, the long waves can’t locate incoming planes. The signal they give might be one plane, several planes, or even a flock of geese.

The British needed radar that used smaller wavelengths. But no one knew how to make those shorter wavelengths, around ten centimeters long. No one, that is, until two researchers went back to basics.

When the invention that made ten centimeter (microwave) radar possible was shown to the Brits’ American allies, I.I. Rabi took one look and said, “It’s simple. It’s just like a whistle.”

Short wave radiation (microwaves) have more energy than long wave radiation. Visible light has more energy than microwaves. Ultraviolet has more energy than visible light (that’s why it can give you a sunburn). X-rays have more energy than ultraviolet. And so on. If you think about it that way, then creating microwaves is harder than creating long waves. But Rabi and the British researchers had both looked at the problem in another way.

A whistle isn’t much of a musical instrument. Unlike a clarinet or a flute, it gives a single tone. Change the size or shape of the whistle, and you change the tone. But tone is to sound exactly what wavelength is to radio, microwave, ultraviolet, etc. And, as Rabi saw, a whistle is to music exactly as a microwave producer (called a cavity magnetron) is to microwave radar. No matter how hard or soft you blow into your whistle, the same sound comes out. No matter how much or how little energy you push into a cavity magnetron, the same microwaves come out.

With this new invention, the Allies found the German planes, found the German U-boats, and won World War II. You might have used that same cavity magnetron to heat up your chocolate chip cookies this evening. After the war the cavity magnetron became the heart of the “radar range,” what we now call the microwave oven.

Here’s the point. If you start off trying to defeat the Germans, much less warm up your cookies, if that’s your behavioral outcome, how in the world do you start with whistles? The only chance of getting there is to be curious about everything, to build a basic understanding of how the world works, of how ideas like waves (radio waves, sound waves, water waves), atoms, and energy help us organize the world. You can’t just push buttons, like adding ingredients to a sandwich.

Instead you plant seeds, like the whistle idea someone once planted in I.I. Rabi’s mind.

You never know what might grow.