This is something I do NOT recommend, primarily because the feedback you are receiving is not coming from someone with ample experience preparing applicants to gain admittance to the school you are applying for. This kind of perspective is important, and is what you should be aiming for when it coms to live practice.
Having said that, I am aware that a lot of my clients do use a regular English teacher (in most cases RareJob.com) for general English communication practice. This is great! Some use their teacher for interview practice. This is less than great, especially if the English teacher does not have relevant experience or is aware of the MBA interview (and entire application) process.
Here is a way you CAN use your English teacher when rehearsing for an interview:
(1) Give your teacher a bunch of questions that your target school has asked in the past.
(2) Ask them to ask you these questions. Ask your teacher to listen carefully to your answers, but not to give you any feedback on any of them.
(3) After doing a few of them, go back and ask the teacher to recall for you the key details of your answers to a previous question (ideally core content like your career goals or why you need an MBA).
(4) Listen to what kind of information you get back and decide how effectively you are getting across your message. If what they say back to you is not what you are intending to get across, ask questions as to what might have been clear, and what detail may be lacking or where further explanation is warranted.
What you are doing here is practicing. Of course, before practice you need to devise contents. What stories are best? What details show the best fit with a program? What's the right balance of work and non-work content? Such strategic planning is something you should do with someone familiar with the process, and experienced at advising as to what strategies are effective for you when it comes to answering interview questions.