A new strategy for adding and subtracting integers

We have an intervention class that only has 16 students in it; these students did not meet standard on the 6th-grade state test last year, so all of them struggle with math.  While working with these seventh-grade students, I noticed that they frequently confuse adding and subtracting integers when both positive and negative numbers are involved. When I posed 5 + -7 =?,  students answered 12, -12, 2 and -2.  When I asked students for their strategy, one student said that he thought of -7 as -5 + -2, and then cancelled 5 and -5 since he knew that every number added to its opposite is zero, so the answer was -2.  This strategy helped other students to solve additional problems and decide if the answer should be positive or negative. My teacher and I decided to show this technique to our seventh grade math classes on the following day, so that kids that get confused with adding positives and negatives would have an additional method to solve those problems, as well as a check on whether their overall answer should be positive or negative.