hmm I am Japanese and used to go to ordinary schools in Japan.
What I imagine is like...when a new student joins a class, he or she is assigned to a desk/a chair and told to sit there before a class stars?
Or maybe he/she will enter the class with the teacher...sorry I think it just depends on each school.
And then, yeah I think the new student is requested to introduce himself/herself in front of the entire class.
I think it all depends on what the student wants to say but what I imagine could go like...
Minasan Ohayougozaimasu (Good morning everybody)
Watashi no namae wa ___ ___ to iimasu (My name is ___ ___)
___ kara kimashita (I am from ___)
Watashi no shumi wa ___ desu (My hobby is ___)
Yoroshiku onegaishimasu (#it is actually kind of a tricky phrase but it could be translated like: Nice to meet you/Please be nice to me)
"Take a bow" and they will know you are done...
ooo sorry it's just an imagination...maybe somebody else can give you a better example...