As if that weren't bad enough, a recent confidential report commissioned by former Education Ministry Xavier Darcos revealed that substitute teachers registered even higher levels of absenteeism than the people they were meant to replace. 17.4 days a year!!
As a result, 10,000 classes currently have no teacher at all.
For the full report, read the excellent article in Le Monde entitled "Two million sick days" by Maryline Baumard.
On a personal note, I remember watching an 8th grade class self-destruct over the course of a year during which the French --and home room--teacher was absent and not replaced for over a month. During that time, the kids had "perm" (left to their own devices) with no French whatsoever. At each "conseil de classe" the other teachers and the principal complained about how dissipated and disruptive the students were. But at no point did it occur to them that abandoning the kids for over a month had anything to do with this.