What's wrong with my scale script?

So what's wrong with it? The ground will instantiate, but not scale.

var ground : GameObject;
var roadLength : int = 15;
var numberOfRoads : int = 10;

function Start (){

Instantiate (ground, Vector3(-10,0,-10), transform.rotation);
transform.localScale.x = numberOfRoads * (roadLength+35)+200;
transform.localScale.y = 100;

}

You are scaling 'this' object, not the one you instantiated. Try

var newObj = Instantiate (ground, Vector3(-10,0,-10), transform.rotation);
newObj.transform.localScale.x = numberOfRoads * (roadLength+35)+200;
newObj.transform.localScale.y = 100;

Your code should be something like:

var clone : GameObject;
clone = Instantiate (ground, Vector3(-10,0,-10), transform.rotation);
clone.transform.localScale.x = numberOfRoads * (roadLength+35)+200;
clone.transform.localScale.y = 100;