When I learnt Maori I always wondered why the word 'ako' means both to teach and to learn because I really thought they were two different things - there was teaching and there was learning.
However, of course, it makes huge sense - simply one does not exist without the other. And that makes sense of that saying - If you have taught something and the students haven't learnt it then you haven' t taught it. The ONLY response you can have as a teacher is to INQUIRE from the students where the gap is and once you have discovered that, to fill the gap -that's what teaching is.The next step, and the one we sometimes let go is to make SURE in your next planning that you work to mitigate against the same thing happening again because that is what perfecting the art of teaching is.
Teaching really is inquiry.