This is one of my FAVORITE lessons to do with my middle schoolers. At the end of the year this is the activity that most of them remember. In short, we find the measurement of real cars using matchbox scale models.
This lesson has been tied to the Common Core Math standards and would be appropriate for students in 6-9th grade depending on their ability level.
The lesson includes the standards, a procedure and student worksheet. As well as some tips and techniques I use to "sell" it to my students.