Ana next asks Yamilka to share her strategy. Yamilka has made a mistake in
her strategy and has come up with the answer of 26. This is what she writes on
the board:
This is actually her second way of doing the problem. She had gotten the incor-
rect answer of 26 using her first method, and she is trying to make the second
strategy equal 26 because she knows that the answer to a problem is supposed to
be the same no matter which strategy is used.
Ana asks a series of questions to help her better understand Yamilka’s think-
ing and to help Yamilka identify and work through her mistake. For example:
- Ana asks Yamilka, “Why did you add 8?” to help Yamilka reflect on and
voice her reasoning. - Ana asks, “Are you taking 48 children out of the bus? Did you take these
8 children out of the bus?” Does Yamilka think she has taken away all 48? - Ana asks, “Where do you think you messed up? Why do you think so?”
Does Yamilka recognize her mistake and does she understand why it is a
mistake? - Once Yamilka changes her answer to 14, Ana asks Yamilka if she knows
that answer is correct. She asks this perhaps to see if she is choosing that
answer because others got to that answer or because she had a strategy to
figure it out. - After Yamilka has identified and corrected her mistake, Ana asks, “Why
did you make that mistake? What can help you not make that kind of mis-
take again?” Does Yamilka understand her mistake? Can she generalize
what she now understands to think about how she could prevent a similar
mistake?
Ana and the other students help Yamilka work through her mistake. The students
ask Yamilka why she added on 8, and a student points out a computation error.
Ana asks her to look carefully at what is happening in the problem and whether
that matches what she did. Together they look at specific numbers to see if what
Yamilka did matches the action of the problem. Finally, Ana asks Yamilka to
name her mistake and think about preventing a similar one in the future.
From the questions Ana asks Yamilka, it is possible to gather some informa-
tion about what Yamilka understands about subtraction and numbers in general.
She understands that the problem is a subtraction (removal) problem. She knows
− 1062 52 42 32 22 26− 10 − 10 − 10 + 8How Many Children Got off the Bus?