Общий вопрос: Has he been teaching children all his life?
Альтернативный вопрос: Has he been teaching children or adults all his life?
Вопрос к подлежащему: Who has been teaching children all his life?
Специальный вопрос: What has he been doing all his life?
Разделительный вопрос: He has been teaching children all his life, hasn't he?