The interview was supposed to be a group interview (my particular interview was supposed to have 3 people including myself), however the other applicants did not show up, so I ended up having a one-on-one interview. So, I am unsure if the interview would have been different had it been in a group format. I suspect it would be mostly the same, except that all the candidates would be asked the questions, and you wouldn't have as long to answer the questions. For the record.... if you aren't going to show up, call first!
It was fairly casual, and I felt very at ease with the interviewer. Present yourself as outgoing and enthusiastic right from the beginning and it will give the right impression. They ask you to prepare a short (2-3 minutes) demonstration where you bring in a science experiment and explain/present it as if you were explaining it to children. She asked me to do the little presentation somewhere in the middle of the interview. They will also give you some time to set up your experiment if you need it.
Just another note-- maybe avoid bringing vinegar and baking soda for your interview demonstration... they have seen that one a million times! However, the demonstration is more about how you present yourself and explain the material, rather than the experiment itself, since in the actual job they provide everything for you.
I believe there are 4 training sessions you have to attend after you are hired to learn the job (if I remember correctly there's an orientation, general training, birthday party training, and class management training), which you are paid for.
Another note... as far as I know, they will not accept employees who have worked for Little Ray's/Radical Science, as they are in direct competition.