$file = APP_DIR .'/test.xml';

$xml = simplexml_load_file($file, NULL, NULL, "http://schemas.xmlsoap.org/soap/envelope/");
$ns = $xml->getNamespaces(true);
$soap = $xml->children($ns['soap']);
$res = $soap->Body->children($ns['m']);

foreach ($res->xpath('//Schedule') as $item) {

    foreach ($item->Name->Groups->Group as $group ) {
        print_r($group->Code->__toString());
    }
}