# Number Rack, by The Math Learning Center

- addition
- numbers
- subtraction

- deduction
- investigation
- prediction

###### Pros

Looks and feels like a physical abacus with responsive controls and familiar layout, while annotation features and variable rows add extra value.###### Cons

Colors are fixed, there's no built-in lessons or guides, and there's no satisfying "click" when sliding beads around. Plus, use is totally reliant on teacher knowledge.###### Bottom Line

It's a free, portable abacus that requires a good curriculum to make it useful. Otherwise it's just e-beads.A realistic design with wonderfully responsive controls make this virtual abacus almost as nice as the real thing, lacking only the tactile feel of beads clicking together. Still, it's an abacus, which isn't the most exciting manipulative.

This kind of abacus is great for teaching place value and multi-digit operations, but that depends entirely on the skill of the teacher and the quality of the lesson. It's possible to do some discovery learning with this, but comes with no guarantees.

There's a nice tutorial of all the app's features and a link to to the developer's (paid) curriculum, but for students, there's no mathematical help to be found. Again, this is just a tool, not a complete learning experience.

Incorporate Number Rack into your early counting and place-value lessons to add that great manipulative boost to otherwise tough cognitive jumps. Also, even older kids can benefit from the way it makes multi-digit addition and subtraction so real and present, in a way that carrying and borrowing in tabular arithmetic can't quite touch.

Either way, you'd benefit from a good search for abacus lessons (search for "slavonic abacus", "bead-frame", "rekenrek," and "100-bead abacus" lessons) before jumping into classroom or one-on-one use, because without some support it's pretty tough to discover number properties just by playing around. If you've already got a physical version, go with that first; if you want every kid to have their own to work with, installing this on a class set of tablets would be a smart move.

Read More Read LessNumber Rack is a virtual slavonic abacus (also called a bead frame) with some extra features that make it a more flexible learning tool than the real deal. It features the familiar red and white beads (which can't be re-colored) and horizontal layout of the elementary school manipulative, and beads slide across the virtual rods effortlessly with smooth animation. Groups of beads can be dragged and positioned arbitrarily, just like the real thing.

Unlike the physical version, Number Rack lets users change the number of rows, from just one (to two if you need a 20-bead rekenrek), all the way up to the classic 10. It also includes an annotation tool so you can write notes and circle groups, and an equation editor for adding math right to the screen. There's a built-in shade so you can cover groups of beads in pre-set arrangements.

Read More Read LessThe 100-bead abacus has a long history of elementary school use, and Number Rack's version will work just as well as that real-life learning tool. It's great for teaching place value, counting patterns, multi-digit operations, and grouping, to name just a few applications. This one doesn't have the wonderful hands-on feel and satisfying *click-clack* of physical beads, and there is some emotional, intuitive sense of number lost in the translation to a virtual tool, so don't chuck out your wooden model just yet.

The option to change colors to make it resemble a Montessori-style bead frame, or to color groups of beads arbitrarily for specialized lessons, would add extra value beyond the typical slavonic abacus uses. Also, even a little bit of support for kids and teachers about how to use this fairly specialized tool would be a welcome addition.

Read More Read Less## Key Standards Supported

## Counting And Cardinality | |

K.CC: Know Number Names And The Count Sequence. | |

K.CC.1 | Count to 100 by ones and by tens. |

K.CC.2 | Count forward beginning from a given number within the known sequence (instead of having to begin at 1). |

K.CC.3 | Write numbers from 0 to 20. Represent a number of objects with a written numeral 0-20 (with 0 representing a count of no objects). |

Compare Numbers. | |

K.CC.6 | Identify whether the number of objects in one group is greater than, less than, or equal to the number of objects in another group, e.g., by using matching and counting strategies.1 |

K.CC.7 | Compare two numbers between 1 and 10 presented as written numerals. |

## Number And Operations In Base Ten | |

K.NBT: Work With Numbers 11–19 To Gain Foundations For Place Value. | |

K.NBT.1 | Compose and decompose numbers from 11 to 19 into ten ones and some further ones, e.g., by using objects or drawings, and record each composition or decomposition by a drawing or equation (e.g., 18 = 10 + 8); understand that these numbers are composed of ten ones and one, two, three, four, five, six, seven, eight, or nine ones. |

1.NBT: Extend The Counting Sequence. | |

1.NBT.1 | Count to 120, starting at any number less than 120. In this range, read and write numerals and represent a number of objects with a written numeral. |

Understand Place Value. | |

1.NBT.2 | Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: |

1.NBT.2.a | 10 can be thought of as a bundle of ten ones — called a “ten.” b. |

1.NBT.2.b | The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones. |

1.NBT.2.c | The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones). |

1.NBT.3 | Compare two two-digit numbers based on meanings of the tens and ones digits, recording the results of comparisons with the symbols >, =, and <. |

Use Place Value Understanding And Properties Of Operations To Add And Subtract. | |

1.NBT.4 | Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten. |

1.NBT.5 | Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used. |

1.NBT.6 | Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. |

2.NBT: Understand Place Value. | |

2.NBT.1 | Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones; e.g., 706 equals 7 hundreds, 0 tens, and 6 ones. Understand the following as special cases: |

2.NBT.1.a | 100 can be thought of as a bundle of ten tens — called a “hundred.” |

2.NBT.1.b | The numbers 100, 200, 300, 400, 500, 600, 700, 800, 900 refer to one, two, three, four, five, six, seven, eight, or nine hundreds (and 0 tens and 0 ones). |

2.NBT.2 | Count within 1000; skip-count by 5s, 10s, and 100s. |

2.NBT.3 | Read and write numbers to 1000 using base-ten numerals, number names, and expanded form. |

2.NBT.4 | Compare two three-digit numbers based on meanings of the hundreds, tens, and ones digits, using >, =, and < symbols to record the results of comparisons. |

Use Place Value Understanding And Properties Of Operations To Add And Subtract. | |

2.NBT.5 | Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction. |

2.NBT.6 | Add up to four two-digit numbers using strategies based on place value and properties of operations. |

2.NBT.7 | Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three- digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds. |

2.NBT.8 | Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900. |

2.NBT.9 | Explain why addition and subtraction strategies work, using place value and the properties of operations.3 |

#### See how teachers are using Number Rack, by The Math Learning Center

#### Teacher Reviews

- A Virtual Abacus for the Internet Age4July 10, 2016