Benchmark 4B
The Physical Setting: The Earth
Grades 6-8, page 68

We live on a relatively small planet, the third from the sun in the only system of planets definitely known to exist (although other, similar systems may be discovered in the universe).

NSES Content Standard D
Earth and Space Science: Earth in the Solar System 
Grades 5-8, page 160 
The earth is the third planet from the sun in a system that includes the moon, the sun, eight other planets and their moons, and smaller objects, such as asteroids and comets. The sun, an average star, is the central and largest body in the solar system.