How has the timing of leaf fall changed over time? Engage your students in tracking leaf coloration and leaf drop in the trees in their backyards or schoolyard. After completing this activity students will be able to explain why trees change color and measure the timing of leaf color change and leaf drop. This activity provides you with an introduction, student worksheet and instructions, a student datasheet, and a slideshow to teach students basic tree identification. There are also links to resources about the science behind leaf color change. Students will graph their results and compare them to several decades of phenological data gathered by scientists at Hubbard Brook Experimental Forest. Students will spend 20 minutes, ideally twice a week, outside gathering their data over the course of a month or so. If possible, begin this activity just before the leaves have started changing color.