get music from the time when the person was at school. wear uniforms. use chalk to write things on floor or walls (say fence or something). things like tom & ema 4 eva sort of thing but use names of your friends. serve food in lunch box say instead of serving them on a plater.

have you got the music for that time to play ,, download them off the net ?/

scan some pics of the school days and print them out and put them up .

stick up  the school reports if you still have them ,,you might be able to find info on the school on the net both my schools are on the net also ...

just go to google search and type in your schools name you should also be able to get pics off there as well , make it a dress up party as in school uniforms

how about asking the poeple you invite if they have any  schoo; photots of themself and  put them up  on a board  .

How about having slow dances at the end where you are not allowed to touch (ie: kiss, fondle etc) the partner you are dancing with - just like it was when I was at school. You could get someone to pretend to be the head teacher to police everyone!

How about having a tuck shop theme for the food?