[Plugin dev] Plugin activation issue : unexpected behavior

Hi! I am encounterig problems developping a plugin. I use a hook to call a function when the plugin is activated, it seems to work but it doesn’t call the sub-functions called in this function. Let me show you the structure of my code:

class aixorder{

	function aixorder(){
		register_activation_hook(__FILE__, array(&$this, 'aixorder_activate'));
		return true;
	}

	/* Plugin installation */
	function aixorder_activate() {

                /* some actions that are well executed */

                /* this call is not done ! */
		$result = $this->calculate_all_scores();

		return $result;
        }

        function calculate_all_scores(){
        /*blabla...*/
        }
}
$aixorder = new aixorder;

It seems that activate_aixorder() is called and executed, but then calculate_all_scores() is not !
I really don’t understand, because when I call it manually by doing this, it works fine and calculate_all_score() is well executed:

class aixorder{

	function aixorder(){
		register_activation_hook(__FILE__, array(&$this, 'aixorder_activate'));
		return true;
	}

	/* Plugin installation */
	function aixorder_activate() {

                /* some actions that are well executed */

                /* this call is done ! */
		$result = $this->calculate_all_scores();

		return $result;
        }

        function calculate_all_scores(){
        /*blabla...*/
        }
}
$aixorder = new aixorder;
$aixorder->aixorder_activate();

So I guess there is something in the activation context I did not understand, as anyone an idea ?

Thank you for your help !