Display a specified content on a Page and all its child pages

You can do that by using this nice little function:

function is_page_or_child_of($slug){
    global $post;
    if (empty($slug))
        return false;
    //is it the page?
    if ($post->post_name = $slug) 
        return true;
    //check the children
    $page = get_page_by_path($slug);
    $children = get_pages('child_of=".$page->ID."&sort_column=post_date&sort_order=desc');
    foreach ($children as $sub){
        if ($post->ID == $sub->ID){
            return true;
        }
    }
    return false;
}

and instead of using is_page('our-school-district') use s_page_or_child_of('our-school-district')