It sounds like the new school is great

and hooray for Mika taking charge of getting glasses and making a fresh new start. As for the old principal, she is doing nothing but backpeddling, trying to cover her own backside as she has allowed this teacher to abuse kids for years and has done nothing about it. I would try making an outline of the things you want to say to her. Don't take any crap off her and tell your advocate that you want her to help end the interview if the principal starts blaming you or your son. End it simply by saying something like, "I came to tell what this teacher has done. Now I am finished. Please have my children's records sent to the new school. Thank you, Good-bye". Then leave. You put the fear in her when you sent copies of your letter to all the powers-that-be. She is worried for her job, not worried about doing right for your kids. You can copy this and send it to her if you like. I will be excited to here how things go at the new school.