I am not sure which country you live in since your profile only says "earth." So I would check your local laws, but I would say it is not true if in the USA. I believe Federal Law 18 U.S.C. 2511(2)(d) would require the consent of at least one of the two parties of the Facetime call to have given consent to be recorded. So I think hijacking or deceptive practices such as replacing facetime with an imposter app in order to record would be problematic for the school.