App review by Debbie Gorrell, Common Sense Education | Updated June 2014
Montessori Math: Add & Subtract Large Numbers
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Montessori Math: Add & Subtract Large Numbers

Solid interactive tool targets regrouping with 3- and 4-digit numbers

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Subjects & Skills
Math, Critical Thinking

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Pros: Engaging activities and interactive features make learning about addition and subtraction fun.

Cons: Students don't get detailed feedback when they get an answer wrong.

Bottom Line: With three approaches to learning that progress in difficulty, a practice toolbox, and fun games, this is a solid resource for teaching kids how to add and subtract large numbers.

This would be an effective tool to use with students who already know how to add and subtract two-digit numbers. They should also have some basic knowledge of the hundreds and thousands place values before starting. For reinforcement, have students work in pairs using the Toolbox to practice making large numbers. Then they can apply what they practiced by playing the stamp game. As students get more confident with regrouping and carrying, have them use the bead frame and eventually the magic slate. It could be fun to incorporate the Playbox games into lessons as well, and have students share the silly monsters they create as they earn points.   

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Montessori Math: Add & Subtract Large Numbers is an interactive math tool that teaches students how to add and subtract three- and four-digit numbers by focusing on the concept of regrouping units. At the home screen, students tap the desired operation icon to choose either addition or subtraction, then choose the stamp game, the bead frame, or the magic slate. The stamp game and the bead frame use place-value decomposition to help students practice regrouping and carrying when they add or subtract large numbers, and the magic slate offers them the opportunity to work in columns, one digit at a time. When students return to the home screen, they can access a Toolbox and a Playbox. In the Toolbox, they practice using the stamps and bead frame to make numbers. In the Playbox, they apply what they've learned -- as well as take on more challenging problems -- by playing three different games. In "Missing Digits," kids have to find missing digits in addition and subtraction problems. In "Wiz Quiz," they get timed, random problems to solve. And in the "Bubble Game," they drag the correct bubbles into place to complete problems. Students earn points, which they can use in the Monster Lab to buy body parts and build a silly monster. Other features of the app include the ability to add multiple user profiles and customize settings, including choosing a language, turning off the sound, and setting parameters on the numbers used in the math problems.  

Students should at least be able to read two-digit numbers prior to using Montessori Math: Add & Subtract Large Numbers. In the stamp game, students break numbers into place values using "stamps" arranged in columns, and then either add or take away stamps to get the sum or difference. This approach helps them understand the concept of regrouping and carrying, as does the Toolbox activity in which they practice decomposing numbers using stamps. When students use the bead frame, they continue to work on regrouping and carrying, but they have to carry over more often because there are fewer pieces for each place value. When students use the magic slate, they apply the more traditional approach of working in columns. The learning progression is excellent and can be customized to fit different levels. Students don't have to complete one area of instruction in order to use the next one, so they can start anywhere they like and move among different areas as needed. 

Overall Rating


Cute and colorful graphics are appealing, and students will be engaged by the interactive drag-and-tap games. 


Unless the level is manually changed, users begin at level 1 and build to level 4 through successful gameplay. Games, practice activities, and interactive tables allow kids to apply and assess learning. 


An adult section explains the learning concepts, recommended prerequisites, and how to customize the app using the settings. 

Common Sense reviewer
Debbie Gorrell Educator

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