PARIS — Every country has its back-to-school rituals. In France for the past few years, la rentrée — the return to classrooms after the two-month summer break — has been accompanied by teacher strikes.

Last year, one in four teachers didn’t show up for work on some September days to protest against changes in the school timetable. The year before, some struck because of losing a day’s vacation. This year, the largest teachers’ union has called for a daylong strike next Thursday and a mass rally in October to voice discontent with the government’s plans to alter the middle school curriculum. Among other things, there will be fewer possibilities to teach Latin and German, and a new emphasis on interdisciplinary studies.

It is easy to accuse the teachers, as some do, of blocking any attempts to improve the system. It’s also easy to understand why teachers are fed up. They are poorly paid by European standards. They operate within a stifling, highly centralized hierarchy that micromanages their every move. And for more than a decade, they have borne the brunt of constant but minor reform attempts that have singularly failed to address the two critical issues facing the French public school system: the rapid decline in the academic performance of pupils, and the growing social inequality in the education system.

Today, one in four pupils in France fails to complete his or her secondary education, according to the national statistics office Insee. In the international PISA studies that measure the performance of 15-year-olds around the world in mathematics, science and reading comprehension, the average French score is at best mediocre, and the number who perform poorly has risen sharply since the first test in 2000. Even the top performers are less numerous as a percentage of the student body than in other European countries including Germany, Poland and Belgium. For a nation that long believed in the intellectual excellence of its school system, that’s painful.