V.P.
Oh my gosh! I've been going through the exact same thing for the last 2 days! My younger daughter just started 3rd grade and already wants to go back to 2nd! She thinks her teacher doesn't like her and she talks too fast! She thinks the other kids don't like her and that she's the youngest in her "whole grade" (she's a June bday, but not the youngest in the whole grade). She totally had a meltdown last night.
One mom who saw my daughter going through this suggested that she's may be very tired. Starting a new schedule, and having demands all day can ware out an 8 year old.
I'm going to hold off talking to the teacher, and hope that things work themselves out. We'll also be scheduling playdates with her new classmates (none of her best friends are in her new class, which makes it even tougher).
Good luck!