populate new admin column with meta value

I’m a bit stumped with this… I have a new column (att_order) in the admin post list for a custom post type (attorneys) and I want to populate it with the values from a custom meta key (_att_meta_order). This is as far as I got:

add_action('manage_attorneys_posts_custom_column', 'manage_att_custom_columns', 10, 2);
function manage_att_custom_columns( $column, $post_id ) {
	global $post;
	switch( $column ) {
		case 'att_order' :
		$att_order = get_post_meta( $post_id, '_att_meta_order', true );
		break;
	}
}

And me being here means it doesn’t work! The column remains empty. What is the correct way to grab a meta value for a column? Any help appreciated.