Subtraction - Equal Change- Stations (1)

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SWBAT explain and use the equal change algorithm to solve 3 digit subtraction problems.

Big Idea

Alternative algorithms open up doors to productive alternative thinking.


5 minutes

I explain to students that they will practice the equal change algorithm in several different ways today.  

At the Teacher Station, I will work with them in a (relatively) small group and watch them work through problems on whiteboards to address their specific questions, strengths and struggles.

At the Fact Fiesta station, they will work on adding two digit facts as fast as possible.

The 3rd station is Student Teachers.  At this station they will take turns teaching a problem to the group and the rest of them pretend to be the students.  They can ask student questions and an occasional silly student question as long as they stay on task.

The 4th station is the Opposite Teams station.  They work on a set of problems and one student is the designated decision maker.  That student decides what change they will make at each stage of the problem.  Whatever operation the leader chooses (add 3), the partner must do the opposite (subtract 3).  They work down their respective sides of the equation and switch roles for each equation.

In my classroom I had a 5th station because I wanted the students in small enough groups so that my time with them at the Teacher Table was meaningful.  (I have 30 students).  The 5th station was a computer station, where they were allowed to work on incomplete math assignments, (we have a required online program), individual work in their Google Drive account, or teacher selected math sites.  Another alternative would be to have the students at this station read math books, work with pattern blocks, or write and solve 3-digit addition and subtraction word problems.

Station Rotations

55 minutes

The groups stay at each station for 20-25 minutes, and I spend the first 5 minutes walking around and reminding everyone of what their task is at each station.  I also revisit the groups when they make their transition, and remind everyone that they rotate clockwise.  I build in 5 minutes for that overall because the time spent there means I can be 90% focused on my group at the Teacher Table.  They work through their first problem while I'm making sure all the other groups are operational.

At the Opposite Teams station, I've provided space on the printed page but this work can be done just as well by copying the equations from a board or the paper and working on scrap paper, in their math journals, or even on a whiteboard if you know they will hold themselves accountable.

Student Teachers can create any problem they want to when they teach the class, though it is suggested that they use a 3 digit problem.  The class can work along with the teacher to increase accountability and engagement.

For the Fact Fiesta station,  students work through a series of fact practice pages.  First they work on basic facts and if they have mastered that (can complete a page in less than 4 minutes) then they move on to subtraction equations with minuends of 20, 50, and 100.  They fill in their own record-keeping page (with monsters) to track their progress.  Math Fact Cafe and Worksheet Works are just two of many available basic fact/equation generators.

 When creating the groups for this activity, I use my notes/observations/student work to group them approximately by level.  It's not an exact science but I try to avoid having a student still working with 2 digit equations in the same group as one of my students that needs extension to 5 or 6 digit or other additional complexity and conversation.  Then, when I work with them at the Teacher Station  I am, ideally, making up no more than 2 versions of problems for them to work through at any given time.  This makes my interactions with the students more efficient and meaningful.  I create the equations as I work with each group, and if they are one of the groups who has turned in work from previous stations, then I can also get ideas from their errors or areas of strength.