What's with that clock change thing?

One of the best projects my classes have ever done has been participating in Mystery Class through Journey North. In this global game of hide and seek, the search is on to discover the location of 10 mystery class locations somewhere in the world. Hundreds of classrooms participate in this project ranging from second grade through 12th grade. 
We start prepping for this hunt the first week of school by noting the sunrise and sunset times in our city. How many hours of daylight do we have? Next week, will it be the same, or different? Why is it changing? Each week we look up this data, graph it, talk about it, wonder what it means. We discuss and think about time zones - why is it later when we call grandma on the East Coast? We trace our shadows at differnt times in the day, why are they longer shorter, going this way or that?
In January, we will start getting sunrise and sunset times for the 10 mystery locations. Based on what we've observed in our local area, we will make predictions about where these sites could be. Later we'll get some more data and geographical clues to research, narrow down, and hopefully confirm our guess. We will be right? Even I, the teacher, don't know. But finally the true locations will be revealed. Whether we are right or wrong doesn't matter as much as the quest and learning. But we are usually right ;)
Which brings me to my original question, what's with this time change thing? This week, while charting our daylight hours and the sunrise and sunset times, we noticed something strange. The pattern of change for the daylight stayed the same, we are losing about 13 or 14 minutes of daylight each week - this week about 10 hours and 46 minutes of daylight here. But the graph for the sunrise and sunset times took a big jump to the left. What happened there? Our entire class was able to connect that changing the clocks made our graph have a big change. It didn't change the amount of daylight, we didn't actually add or lose an hour, it just stepped to the left (or moved to the morning.) 
(I forgot to take a photo of our working graph. I'll do that tomorrow and add it here.)