ActionScript 3.0 :: Board Class - Capturing Mouse Click

1. I create a board class in board.as as so,
public class board extends Sprite {
public function board(p1:Number = 0, p2:Number = 0, p3:Boolean = true) {
this.mouseEnabled = true;
addEventListener(MouseEvent.CLICK, go);
} private function go(e:MouseEvent) {
trace("mouse clicked");
}}

2. In .fla, I declare the document as an instance of the board class.
3. Clicking anywhere on the document's UI, no tracing output.
4. If I put a textfield as the child of board object (by adding these lines,
var tf:textField = new textfield();
---
addChild(tf);
In the constructor), I do see above trace() working.
What am I missing? How can my board class receive mouse click?