Violin- the smallest and highest sounding of the string orchestra instruments. Easy to transport to and from school.
Viola - a little larger and lower sounding. A more mellow sound, and also easy to transport to and from school. Go to the videos to see a demostration of the difference between violin and viola.
Cello- much larger and deeper sounding. Requires ability to transport to and from school, as it takes up much more room . More expensive and the schools have less of them to lend.
Bass- This instrument is VERY large and very deep sounding. It requires extra effort to play, as the strings are larger as well. Students need a safe place to keep one at home. Extra practice is essential, so serious 6th grade students only.