There is always something new to find out about Rudolf Steiner.
According to James R. Lewis in his book Witchcraft Today: An Encyclopedia of Wiccan and Neopagan Traditions, Rudolf Steiner headed a chapter of the Ordo Templi Orientis (OTO) in the early 20th century before he founded the Anthroposophical League.
“It is this common background in magic that seems to explain why Waldorf schools celebrate the same eight Sabbats as Neopagan witches” says Lewis, p 215.
The OTO has the Law of Thelema as its central religious principle and was disbanded and banned in England in 1923, due to the notorious activities of Aleister Crowley when he was perfecting a system of sex-magic in Sicily in the early twenties. It was originally modelled on Freemasonry, according to wiki.
The law of Thelema is “Do what thou wilt shall be the whole of the Law. Love is the law, love under will.”
Before her untimely death this year Peaches Geldof apparently (according to the Guardian) tweeted a picture of a book by Crowley and sported the initials OTO on her body.
Here is a diagram of the eight Sabbats, and there is an explanation of the way they are celebrated by some people including Waldorf schools on the Patheos website.
And the Roots of ritual website which offers advice for Pagans on writing and performing spells and rituals, explains Mabon and its significance, and how Waldorf schools celebrate it.