The most effective way to teach second graders about place value and base-ten addition is to guide them through hands-on lessons of grouping numbers into thousands, hundreds, tens and ones. Physical manipulatives, such as blocks, are ideal for these types of activities, but interactive online games that use virtual manipulatives are useful as well--and are sometimes more practical.

## Grouping Place Values

Split the class into groups and give each group a box of Lego blocks. Explain to the class that every two-digit number is simply a combination of groups of tens and a group of ones. Then demonstrate how this looks by building a column of ten blocks and a column of only a few blocks. Next, write a two-digit number on the board and instruct the groups to try and build the number. Go around the room and help each group assemble their columns. You can also encourage students to count the columns by tens and ones, as well as counting every individual block, so that they can see for themselves that the numbers are the same.

## Regrouping Numbers

When your students have finished building the number with the blocks, write the number on the board as tens and ones. For example, if the number you originally wrote was "45," now write "4 tens + 5 ones = 45." Below this equation, write "3 tens + 15 ones = ?" Ask the class to rearrange the numbers so that the ones are less than 10. Encourage them to use the blocks to help find the answer. As they work, they will see that "3 tens + 15 ones" is the same as "4 tens + 5 ones" and that they both equal 45. Afterward, give students new numbers to regroup into tens and ones (See Reference 2).

## Numbers and Nuggets

Give each student a collection of plastic numerals, a bowl of chocolate-covered raisins and an empty egg carton. Ask students to place the plastic numerals in front of them on their desks, and then write a number on the board. Next, have students split the numerals into tens and ones by moving them apart. Then, instruct students to fill the compartments of their egg cartons with the appropriate groupings of chocolate-covered raisins. For example, if the number is "28," they should fill two compartments with 10 raisins each and one compartment with eight raisins.

## Activities for Higher Numbers

While using manipulatives for teaching place value is effective for two-digit numbers, using them for three- and four-digit numbers could be too time consuming. To teach the place value of higher numbers, use online activities that can display virtual manipulatives without the hassle of assembling them or having to clean them up afterward. For example, IXL.com offers place value games for second graders that display groups of blocks up to the thousands. Also, ABCya.com offers a game called Base Ten Bingo that has players add groups of manipulatives and select answers from the spaces on a bingo board. When players get a full column or row of correct answers, they win the game (See References 2 and 3).

#### References

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