France has been experimenting a 4-day week for primary school since the 80s [1], generally with a day-off on Wednesdays. The impacts are certainly there, e.g. "before September 2013, more than 40% of mothers whose youngest child was of elementary school age did not work on Wednesdays".

It sounds like a 4-day school week would be the natural consequence of a global 4-day working week.

[1] https://fr.wikipedia.org/wiki/Rythmes_scolaires_en_France