Success is when you are in a personal stable situation yourself so that you are able to help
others. There is nothing you can give if your own basket is empty.

If you are in a classroom with students and you have some educational training, at the moment in location and time, you are always in a position to help others in their learning process.

If you are generous with your ability and possess compassion, I consider that effort a success.

Your housing may be worse than a developed nation's prison. Your income may not feed you in London. Your transportation may be a bus crowded with people whose language you cannot understand. None of that diminishes your contribution.

The life of the student you mention is testament to your success, Professor. I'm sure there are many.

If a teacher has taught for several years and does not have a legacy of such students... that is the definition of 'deacher'.