Why Is School Choice Not Good for All?

Recently Randi Weingarten, President of the American Federation of Teachers, stated that President- elect Barack Obama has "every right to make a decision that works for their family" when asked if he and wife Michelle should send their children to public schools.   

Why is this typically not the message we hear from the teachers unions when referring to the average American family?  Doesn't the average family deserve school choice as much as the Obamas?  Shouldn't they have the right to make decisions that work best for their family?