According to the 80s Rewind website, about two years after this movie actress Sylvia Kristel appeared in Private School (1983) "only as a contractual obligation to the producers of this movie. She had previously worked with them in another "Private" movie . . . Private Lessons (1981)".
Near the beginning, after Philip is watching Sylvia through binoculars he is looking through a fashion magazine with half-naked women. The model he is looking at in the pages is Gia Carangi, who was a famous model in the early 80s. A film was made about her (Gia (1998)).
The movie was cut and released in a modified version for the film's original theatrical release in a number of territories including the UK and Australia. Around thirty years later, the cut version is still the only one available in both of these markets.
"Although [Sylvia] Kristel bares her breasts frequently, an unmatched stunt double [Judy Helden] is used for her disconcertingly in several of the nude scenes" according to show-business trade paper 'Variety'.
The movie was a "surprise box-office hit" according to film critic Leonard Maltin. Moreover, Allmovie concurs and states that "surprisingly, Private Lessons (1981) was a box-office hit at the time of its release".
Publicity for the later movie Private School (1983) did sometimes, rightly or wrongly, report that it was a sequel to Private Lessons (1981). Both titles had title similarity, the presence of actress Sylvia Kristel, the same producer R. Ben Efraim, and American video distribution through MCA/Universal.
"Philly" (Eric Brown) was the name of one of this 1981 movie's lead characters, "Philly" also being the title of this movie's source novel. This picture was made and first released in the same 1981 year as the similarly named film Chu Chu and the Philly Flash (1981).