Yes it will work, your usb is probably fat anyway, wich is writeble and readable by both Windows and Mac OS.
Now, you need an application to open your file in MAc OS, just like you use powerpoint in windows. Maybe you school have "powerpoint for Mac" installed. If not, openoffic.org is a free suite tha will open your file. There is even a possibility that "keynote", wich is part of "iWork" will open your file, your scholl may have that installed as well.