Satan's School for Girls (1973)
Long story short, the art teacher is Satan and he is recruiting 8 (odd number) girls to replace the 9 he lost years ago. The school burns down but "Satan" gets the last laugh and fades out while smoking a cigarette.
There is no obvious use of magic here.The girls could be in his thrall due to a psych experiment or any number of mundane explanations. I kinda wish there had been more though. Kate Jack's character, Debbie, mentions having Power (yes with a capital P) but nothing ever comes from that.
There is a remake in 2000 with Kate Jackson as the headmistress and fellow Spelling alum and TV witch Shannon Doherty, but I have not seen that one either. At least the drop the witches down to a more respectable 5.
Not a great movie, but a good one to chill out too.
Tally 5 movies, 5 new (to my surprise)
Of course given this, the remake and fun connection to Harry Potter I HAVE to use this in my games someway. The Salem School for Girls would be a great Witch Girls Adventures location.