/**
  * @return string
  */
 public function actionIndex()
 {
     $model = new Teacher();
     $query = $model->getListWithStudentsCounrt();
     $query->asArray(true);
     $dataProvider = new ActiveDataProvider(['query' => $query, 'pagination' => ['pageSize' => 20]]);
     $this->view->title = 'Учетиля (с количеством учеников)';
     return $this->render('index', ['showMonthFilter' => false, 'dataProvider' => $dataProvider]);
 }