Nah, that will scale it from the middle (so it will scale up as well as scale down). What the OP is asking for is to scale by just moving the top or the bottom.
The simple solution is that you have to scale AND move the object appropriately. If you're using the tween class to do this you have to set up TWO tweens - one that tweens the scaleY property and the other that tweens the y (position) property.
To figure out what the final (destination) y coordinate should be is easy - if you want it to appear that the object is scaling from the bottom only (only the bottom moves) you move the y coordinate DOWN by HALF the new height of the object minus half of the ORIGINALheight of the object.
var myBtn; // this is where you put a reference to your button component or movieClip
var oldHeight = myBtn.height; // AS3
var newHeight = 300;// I'm making this up of course
var newYPosition = myBtn.y + (newHeight / 2) - (oldHeight / 2);
// and then just set up your two tweens on the object.
Hope this helps.
