One of England's greatest actors, Lord Laurence Olivier, was originally considered for the role of Priory. However, David Niven ended up with the role.
Screenwriter David Swift, who in the early 1960s directed "Pollyanna" and "The Parent Trap" for Walt Disney, developed this project for the company and was set to direct it. However, he felt Jodie Foster (then one of the most popular teenage actresses in the country) was all wrong for the part of Casey and stepped down.
Veronica Quilligan was apparently an eleventh-hour replacement for the role of Cluny. Early promotional stills for the film were released to the press with an entirely different young actress standing alongside the cast dressed in Cluny's costumes.