Simplifying fractions

I got to teach all 5 classes yesterday because my CT was at a training; her substitute was helpful, providing me feedback and ideas about teaching math.  He reminded me how we learned to simplify fractions, by writing 15/20 as 5*3/5*4 and then canceling the 5/5.  This was something so ingrained in my thinking that I didn't usually show that step, yet many of our students have trouble with that step.  Usually, when I'm teaching, I'll ask the students if a fraction can be simplified, but I wasn't scaffolding the process with the intermediate step.  Now I'll write that step down explicitly, so it's an instant review for students who have trouble simplifying fractions.