This interactive activity helps a user understand that one concept of subtraction is finding a missing addend. In each scenario, there is a given number of animals and some of them leave or hide, and the student must select the number from four choices that are missing based on knowing how many animals are still there. If a correct response is given, then the family of facts are provided and if an incorrect response is made, there is positive instructional feedback provided.

This familiar game can be played by one or two players taking turns. Players choose to match equivalent representations of numbers, shapes, fractions, or multiplication facts. The game can be played in clear pane mode, or for added challenge, with the windows closed.

This interactive Flash applet contains a progressive range of exercises to sharpen mental math and recall of number facts. Levels include one-digit addition and subtraction within 20, two-digit addition and subtraction within 100, and multiplication up to x5 and x10. The goal is to complete 10 correctly as quickly as possible. An incorrect answer deletes a point, discouraging guessing. At the end of each round the applet reports the time taken and the number of errors.

This interactive Java applet provides students with practice in subtraction and pattern recognition. Starting with four numbers in the corners of an outside square, students find the differences (larger minus the smaller) between the pair of numbers on each side of the square. After correctly completing each square, they repeat the process for the next inner square, until all squares are complete. Students can explore the patterns that emerge as they work toward the center square. Users can choose to work with whole numbers, integers, fractions, decimals, or money. They may also create their own problems by selecting the four starting numbers for the outside square.

This interactive applet contains four puzzles which develop fluency with addition facts and foster logical reasoning. Each puzzle provides a shape with blanks along its sides and diagonals. The user must fill in the blanks with the numbers provided to reach the same target sum along each side/diagonal.

This interactive online game for one or two players provides practice with number facts and builds strategic thinking and pattern discovery. Players choose an operation (addition, subtraction or multiplication) and 100 problems appear in a 10 by 10 grid. They then select problems that match given target numbers while attempting to get 5 in a row in the grid. Users have the option of working for 3 in a row on a 5 by 5 board, and of turning the sound off. This game is a good balance of skill and luck.

This interactive Java game, similar to Connect Four, helps students develop game strategy and fluency with number facts. Two players each try to connect four game pieces in a row (vertically, horizontally or diagonally) before the opponent does by correctly answering problems. For each game players can choose whole numbers and/or integers as well as the operation(s) – addition, subtraction, multiplication, division. They can also select the difficulty level and the time limit for each problem.

This interactive game for one or two players develops students' fluency with multiplication facts, understanding of the relationship between factors and products, and strategic thinking. Players take turns moving markers on a factor list and claiming their products on a board displaying all the products of the numbers 1-9. The first player to claim four in a row wins the game. The factors and number needed to win are customizable. The resource includes links to related lessons.

This interactive online game helps students develop fluency with multiplication facts as well as strategic thinking. The goal is to claim four numbers in a row (vertically, horizontally, or diagonally) on a 6 by 6 game board displaying the products of one-digit numbers. Players take turns moving one of the two factor markers to claim a product on the board before time runs out. This game is part of NCTM's Calculation Nation project. Users may login as a guest and play against the computer, or register (free) to challenge other players online.

With this interactive Shockwave applet students practice recognizing various types of numbers, including factors, multiples, and prime numbers. Each level presents several grids of numbers, each with a specific rule. Users select all numbers in the grid that satisfy the rule. Level 1 involves parity (odd/even) and multiplication facts of 2, 3, 4, 5 and 10. Level 2 includes multiplication facts up to 10 x 10, primes, and square numbers. Level 3 also covers powers of 2, triangle numbers less than 100, and lower cube numbers. A Key Ideas window explains each type of number. Cross Number puzzle printouts are available for further practice.

This interactive online game helps students develop fluency with identifying factors while fostering strategic thinking. A student can play against the computer or against a friend on a 6 by 6 grid containing the numbers 1-36. Each player in turn chooses a number from the board, and then the opponent claims all of its remaining proper factors. A player's score is the sum of all the numbers and factors she/he has chosen. When there are no numbers remaining with unclaimed factors, the game ends and the player with the greater total is the winner. This game is part of NCTM's Calculation Nation project (cataloged separately). Users may login as a guest and play against the computer, or register (free) to challenge other players online.

This activity provides students with an opportunity to recognize arithmetic sequences and at the same time reinforces identifying multiples. The interactivity displays five numbers and the student must discover the times table pattern and the numerical shift. On Levels 1 and 2, the first five numbers in the sequence are given and on Levels 3 and 4, the numbers given could be any five numbers in the sequence. The Teachers' Notes page offers rationale, suggestions for implementation, discussion questions, ideas for extension and support.