I've been through this with both my kids, more so DD. They are now pretty self sufficient when getting ready for school, but I still need to watch the clock and keep them on track with reminders. I've found it helps a great deal
not toallow TV, PC or video games until they are totally ready for school. That gives them an incentive to get ready, but then we had to battle with turning off the TV/PC/video game when it was time to go. A new rule was created: If the TV/PC/video game interferes with getting to school on time they will NOT be allowed at all before school. Being consistent and enforcing this rule was key. Things have been pretty much smooth sailing on school mornings around here.
Oh, almost forgot... DD went through a phase when she really dragged her feet. I had to say, "If you're not dressed when it's time to go, you're going to school in your PJs." One time she was still in her PJs when DS and I got into the van and were getting ready to leave. She came running out all upset wearing her PJs with backpack, clothes and shoes in hand. I drove to school and she had to change in the van in the parking lot at school. She has always been ready on time ever since.