Change the part that failed, then test again

What this lesson teaches: When a design fails, change the part that failed, and test it again the same way.

Video rendering. This video is in the Peps pipeline (about 70 seconds, 140 spoken words). Until it lands, the storyboard below is the video, beat by beat.

The script (narration and what is on screen) — open

#	Narration	On screen
1	In Mr. Park's class, Erin's pencil holder tipped over when the desk was bumped, so it did not meet that criterion. Look where it failed. The bottom is narrow.	Mr. Park's classroom; Erin's tall holder lying tipped on the desk; its narrow bottom glows; chip NARROW BOTTOM; no title slide
2	The top held the pencils fine, so changing the top would change nothing.	the top of the holder glows and fades; chip NOT THE TOP
3	So Erin changes the part that failed. She makes the bottom wider.	the holder upright again; its bottom widens in place; chip WIDER BOTTOM
4	Then she tests it again, the same way. She bumps the desk hard. The holder stays up. Now the criterion is met.	the desk wobbles with three long motion lines; chip HARD BUMP; the holder stays up; green tick; chip MET
5	Suppose Erin had bumped the desk gently instead. Her old holder would have passed. But that changes the test, not the holder. The holder would still tip over in class.	the old narrow holder faint; the desk wobbles with one short motion line; chip GENTLE BUMP; chip THE TEST CHANGED, NOT THE HOLDER
6	So, here's what we've seen. When a design fails, change the part that failed, and test it again the same way. Never change the test to make the design pass.	rule slide reuses the tipped holder and the wider-bottom holder on the bumped desk; rule text
7	Okay, now your turn.	the attached question appears

In Mr. Park's class, Erin's pencil holder tipped over when the desk was bumped, so it did not meet that criterion. Now she improves it.

Find the part that failed

It failed at the bottom. The bottom is narrow.

The top held the pencils fine, so changing the top would change nothing.

Change that part

So Erin changes the part that failed. She makes the bottom wider.

Test it again, the same way

Then she tests it again, the same way. She bumps the desk hard. The holder stays up. Now the criterion is met.

What Erin did not do

Suppose Erin had bumped the desk gently instead. Her old holder would have passed. But that changes the test, not the holder. The holder would still tip over in class.

What could change	Does it fix the tipping?
The top	No. The top held the pencils fine.
The narrow bottom	Yes. The bottom is where it failed.
The test, to a gentle bump	No. The holder is the same, so it still tips in class.

When a design fails, change the part that failed, and test it again the same way.

Never change the test to make the design pass.

Okay, now your turn

One easy question straight after the video: the student answers it to move on.

After the video

A paper cup drips from its bottom. What should change?

Quiz

(a) fluency: a failure and the part to change (three options); then yes / no on changing the test. Fresh contexts, never the lesson's own pencil holder.

Question 1

A paper bridge bends in the middle under ten coins. Its ends stay flat. What should change?

Question 2

A kite crashes. Its tail came loose, and its paper and string are fine. What should change?

Question 3

A bookmark slips out when the book is shaken. Its clip came open, and its ribbon is fine. What should change?

Question 4

A paper bridge bent in the middle under ten coins. Its middle has been made thicker. How should the new bridge be tested?

Question 5

A student says, "My bridge failed with ten coins, so I will test it with five coins instead." Does this fix the bridge?

Question 6

A paper bridge must hold ten coins, using one sheet of paper. A bridge holds ten coins and used one sheet. What should change?

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