Each student needs a place value mat divided into three columns with the headings Hundreds, Tens and Ones and a set of base ten blocks. Use an overhead projector or computer screen to show how to correctly place the blocks during lessons. Before beginning any lesson, students must understand the value of the flats, rods and cubes. Model how to show numbers with base ten blocks by placing them in the correct column. Cubes must always go in the ones column, rods in the tens column and flats in the hundreds column. Show the relationship between the blocks and the written number by writing each number at the top of the correct column. For example, when modeling the number 25, place two rods in the tens column and write "2" at the top and place five cubes in the ones column and write "5" at the top.
Model how to show the number five on a place value mat by placing five cubes in the ones column and writing "5" at the top. Ask students to use their blocks to show the same number. Ask students, "How many hundreds are in the number five? How many tens? How many ones?" Repeat with a few more examples of numbers less than 10. Show students how to show ten by using one rod and placing it in the tens column. Line up 10 cubes next to the rod to show that one rod is worth 10 cubes. Write the number 10 at the top of the columns, placing the "1" in the ones column and the 0 in the tens column. Ask students, "How many hundreds are in the number 10? How many tens? How many ones?" Continue modeling numbers above 10 and asking students to model on their mats. You may use the hundreds column or choose to cover hundreds later, after the students have had more practice.
Divide the place value mat in half by placing a ruler horizontally across it. Use the top of the mat to represent the first addend and the bottom for the second addend. For 25 + 17, place two rods and five cubes at the top of the mat and one rod and seven cubes at the bottom. Begin in the ones column. Ask students to add the cubes on the top and the bottom, getting a sum of 12. Remind students that all tens must go in the tens column, then show how to represent 12 as one ten and two ones. Trade ten cubes in for one rod, then move it to the top of the tens column. The tens column now has three rods on top and one rod on the bottom, and the ones column has two cubes. Add the tens column, bringing all the rods down to the bottom for the sum of 42.
Divide the place value mat in half by placing a ruler horizontally across it. Use the top of the mat to represent the first number and the bottom for the second. For 29 - 14, show 29 at the top of the mat with two rods and nine cubes, then show 14 at the bottom of the mat with one rod and four cubes in the appropriate columns. Begin subtracting in the ones column by taking four cubes away from the top nine cubes. The bottom cubes will not be manipulated, but are there to show which number is being subtracted. Continue with the tens column by taking one rod away from the top two rods. Look at what is left on top to find the difference, 15.