Once upon a time, a long time ago in my previous life in another school district, I participated in some research through ASU. My team teacher and I (we were teaching 1st grade) had a professor from ASU who came in to watch us teach math, specifically, word problems. He was looking at "children's mathematical thinking" and their "mathematical talk." We would pose problems to the students, let them choose their tools for solving the word problems (manipulatives, pictures etc...) and then we would reconvene and share their thinking on the overhead projector (see- I told you it was a long time ago). Well, as we were doing this, the students discovered the matching strategy. I can't remember if it was during a Compare Difference Unknown word problem or if it just came up during something else. Once that strategy was introduced, students started using it ALL the time. They solved almost every word problem using the matching strategy. It was crazy- they loved that strategy and used it for everything whether or not the problem was a compare type problem or not.
So, every year when I get ready to introduce K.CC.C.6 Identify whether the number of objects in one group is greater than, less than, or equal to the number of objects in another group, e.g., by using matching and counting strategies- I worry that the students will overgeneralize with this strategy.
Usually I have nothing to worry about because the kinders usually struggle with compare word problems. They forget the question and just want to join the two group together even after doing lots of hands-on activities where were are comparing tower sizes. Here are two things I am using to help teach this standard this year. This game is in my Kindergarten Math Assessments but I gave it a new, winter twist. In this game, students play in pairs and take a strip of snowmen. Then they use a matching board to compare the snowmen. The idea is that they match them up on the board and the "extras" are the "How many more?" Here's the link to this freebie.