It can be tricky for a lot of students to see the need for bundling.
Often students in early primary (and sometimes later than that) will have an understanding of one to one correspondence for relatively large numbers without also developing the concept of “tens”. Here is a fun task to try when you are introducing the concept of two-digit numbers to kids. I’d suggest you spread these ideas out over the course of a week or two.
Give students a whole lot of pencils, bundling sticks or other long skinny things to count (between 30 and 40 would be about right). Have them start counting. Once they get past 10 interrupt them by asking a question so that they forget where they are up to and start again. Repeat this several times so that they get increasingly frustrated at not being able to keep count. You might need to go as far as knocking all the sticks out of their hands so that they drop them and lose count. The point is to build frustration.
Next, give students some rubber bands (loom bands are ideal) and let them use these to keep track of what number they are up to by creating bundles with the same amount in them. Repeat your earlier questioning and interrupting tricks. Now they should be able to know how many sticks there are because even if they drop the sticks they can easily count in tens to figure out where they are up to.
Next, talk about what ways would be best to bundle sticks. Experiment with bundles of 10. Draw the number of sticks in bundles and left overs. Then write the number in digits. Examine the digits to find how they relate to the number of bundles and left overs. Make connections between the number of bundles and the number of tens. Ask if that same pattern would work for other two-digit numbers. Experiment to see with lots of two-digit numbers.
Finally, talk about what happens to the number of sticks when you add in an extra bundle of ten (or take one off). Kids will probably need to take all the rubber bands off to count the sticks again several times before making the connections.
For more great tasks, check out the book that this task comes from – Fixing misconceptions in addition and subtraction.