to discuss
What is teaching one-to-one in my view?
What makes a one-to-one class successful?

http://www.educaweb.com/noticia/2011/06/27/es-esta-fallando-formacion-ingles-espana-14854.html#respcomok

How many hours do I need to put in to reach a certain level:
https://support.cambridgeenglish.org/hc/en-gb/articles/202838506-Guided-learning-hours