Stop, Look and Check (Part 2)

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Objective

SWBAT determine if they should borrow when solving number story problems.

Big Idea

Learning the process of subtraction is not enough, you need to be able to know when to use it.

Review

15 minutes

We start today by reviewing the idea of stop, look and check. I ask students to copy a double-digit subtraction problem (requiring borrowing) into their math journals. I ask them to use their stop, look and check cards, to stop, look at the ones column and then check the larger digit.  This activity calls student attention to the structure of the problem (MP7). If it is on the bottom, they need to borrow (both bottom and borrow begin with B). If the larger digit is on the top, they do not borrow because it does not begin with B. 

I ask students to complete the problem. I ask for a volunteer to do the problem on the board.

I put up a second double-digit problem that does not require borrowing. I ask the to repeat the process. Again I have a volunteer complete the problem on the board.

Treasure Hunt

40 minutes

To encourage the use of subtraction strategies, I have set up a series of subtraction activities and word problems around the room. Students move from one area to another, solving the problems and gathering the letter or letters that correspond to their answers at each center. 

(I have posted 3 answers at each center, each with a different letter. One of the answers is correct, one is random and the last is one that would be made if students flipped the two numbers around when subtracting instead of regrouping from tens to ones. Students find the answer that matches theirs and writes that letter on their paper. If they collect the right letters, they will end up with the answer to a riddle.)

I explain to students that no more than 4 students can be at a problem center at any one time. They may move from center to center to solve the problems there, but they must then move to an open center. I have more centers than there are students to insure that everyone will always have a place to go to. 

The riddle is "What do ducks use to do their math paper?" Answer: "A quack-u-lator"

The students have a response sheet  that I ask them to put their names on before they begin to rotate around the room.

I remind students to work quietly, talk only to students at their center, and to keep track of their paper. I tell them they may help a friend at a center, but they may not do the work for them or give someone an answer.

I give students about 30 minutes to rotate around the room solving problems. I rotate as well, helping students who may be struggling. 

See: Solving One Problem

Closing

10 minutes

I invite students to return to their seats. I know that not every student will have completed every problem in the room so to give students a feeling of success, I tell students that they can work in teams to solve the riddle. They can compare answer letters, and help each other figure out which letters they have, and see if anyone got one that they need to solve the riddle.  I give students the riddle to solve. I tell them when they figure it out, they should keep it a secret until everyone has had a chance to solve the riddle.

I do collect the papers to see the answers students found for each center. I have a good sense of how students are doing with subtraction because I circulate around the room during the center time noting students who find the work easy or hard.