This is an excellent video to introduce ratios to your students:
And of course to dig further into the concept "The Teaching Channel" provides a great instructional video found HERE!
Another super resource can be found here at Transum.org in which they provide a funny, but relevant "Division in Ratios" slide presentation!
Another fun way to differentiate proportion through art would be to have the students trace their hands and feet and draw a body in proportion to both! This is from Oodles of Art Blog
Another way to practice proportion is by having the students draw a map of their classroom, keeping everything in proportion!
After measuring and cutting out the computer case and all of the components, the students determine how to arrange the parts so that they all fit in the computer case. Then my students add their own personal touches to personalize their computer. This fun project can also be purchased at my TPT STORE, HERE!