I always put LO on a powerpoint and, yes, once you move on it is not visible. Did it when OFSTED in and still got excellent. It is the content of the lesson and learning of students that is important, you refer back to the LO during the lesson. I think you were unlucky as Eva Smith said, interview students are chosen for being good, well behaved students and as there is usually a HOD, Head Teacher, Deputy in the room they should not misbehave. I also think it was mean of the school that you were not allowed in the room before the students so you could prepare yourself, why make it difficult for yo?. If the school have not got the basics of making you welcome on your interview, maybe you did have a lucky escape!