A Melbourne private girls' school that prevented a lesbian student from attending the school formal with her girlfriend is being inundated with messages from irate readers around the world accusing the school of discrimination.

International news organisations have highlighted the case of former Ivanhoe Girls' Grammar School student Hannah Williams, 16, who was barred from attending the formal with her girlfriend Savannah Supski, 15.

News outlets, including the US-based Huffington Post and The Daily Telegraph in London, have compared it to a similar case in the US earlier this year, in which a school called off the annual senior dance after a lesbian student demanded she be allowed to bring her girlfriend.