This is how my students are shown how to do it in their math book.
While teaching this lesson with my first block today, I had a moment of inspiration. I like to pull things in that my students can relate to. Often it deals with sharing with friends and candy. So I got out my counters and we pretended they were candy. One student got counters to note the tens and another student got counters to represent the ones. The third student would ask for for a particular number of pieces.
The student asking for the candy would start with the ones and ask for his number. So using 12-5, a student would ask for 5 pieces from the student who had 2. That student would respond that he/she could not give them that number because they did not have enough.
The student asking would then go to the tens and ask for the same amount. The one with the tens would hand over the requested amount.
We then add what the "tens" student has and what the "ones" student has to come to the answer.
The students really seemed to grasp the idea. I will be interested to see if it has "sunk in" when we go over the concept again on Monday.