Do you see the pattern?

For math class this week our instructor revisited ways to teach students how to add and subtract positive and negative integers.  One method she showed us that I found really clever was to introduce a pattern.  For example:
3 - 3 = 0
3 - 2 = 1
3 - 1 = 2
3 - 0 = 3
3- -1 = 4
3- -2 = 5
3- -3 = 6

If you start with what kids know (subtracting positive numbers from positive numbers) and then move into a more challenging concept (subtracting negative numbers from positive numbers) it helps students to see how the sum is calculated and follows the pattern.  If a teacher then asks students to see if they can identify what is happening when a negative number is subtracted, it is more likely that they'll see the result is addition of that number.

I can absolutely see using this in my classroom and I would be excited to see if the students were then able to come to the conclusion that subtracting a negative number results in adding that number.  I really like this technique.