From there, they chose a photo of a car that they liked.
Instead of drawing a grid directly on the photo, I photocopied a grid on to transparency sheets.
The photo of the car was placed underneath and taped.
Students drew their own grid on another sheet of paper. We used 1/2" x 1/2" measurements for their grid. I didn't have paper large enough to make them bigger. It actually worked out well.
To avoid overwhelming the kids with all of the detail of the car, I found it extremely helpful to have them start with the outline of the car. To do this, we took a vis-a-vis marker and outlined the car. This is nice because it can easily be wiped off and re-used next year.
After they had the outline drawn, they used the vis-a-vis again to outline large shapes. As they continued they outlined more and more. This was a huge help as it simplified the car for them.
Shading was added in the end.
I left it up to the kids whether or not they wanted to erase the grid lines on their drawing.