Not a fan of heterogeneous grouping. Never have been. It's a purely personal choice; I experienced it as a high school student and it was miserable.
But while I believe that tracking is the way to go, I believe there are a couple of ways we do it wrong.
Most commonly we track by the destination. We let students know that Bus A runs to college and Bus B runs to a trade. Each bus runs its own route, and only that route. If students want to ride Bus A, they have to get themselves to the bus stop. Once they meet they bus, the bus can drive them pretty reliably to their destination, but they've got to get themselves from their home to the bus stop, and some students get lost on the way.
Sometimes we track by the students' transportation. This student drives a Porsche, so we put that student on a wide, open highway. This student drives a Yugo with bald tires, so we put that student on a road that is flat and straight. This student drives a rugged SUV, so we send the student up a grinding rough rocky road. And this student is walking, so we put the student on a footpath beside the river. This can seem like a great way to customize the student's travels, but it often fails to consider either where the student starts or where the path leads. We still require the students to find their own way to the starting point, and we don't even think about where the path leads-- just how well the student can travel it.
We often talk about personalizing or individualizing a student's track, but what we really mean is that we make allowances for students to get on the path at different points. Instead of catching the bus at the very beginning of the trail, the student can catch the bus at many different points--along that one route. The students still have to get themselves to the bus stop, and every student is still riding along exactly the same route-- the only difference is how much of the route they travel.
What should we do? Pick up each student at home, meeting each student where he/she lives, drive the student around until the student is ready. Then give each one a gps, a map, and the keys to the car.
Tracking has to consider not just where the trail ends, but where it begins, and how the student is going to travel it. These days, at our best, we tend to just go two out of three. We need three out of three to get really individualized education in place.