School Attendance in Europe

I've been working with European population and education data for the period 1850 to 1993, from B.R. Mitchell's 'International Historical Statistics'.  One thing I've found is that instead of a steadily growing share of population aged 5-19 attending school, the results have been much more variable.  

This makes sense during the chaotic periods, such as the First and Second World War.  But what I can't understand is why the percentage of Europeans in the school-age cohort attending school would be so much smaller today than during the immediate postwar period.  Could this be some anomaly with the data?

Below is an example.  In Austria, school attendance grew until a WWI collapse, and then a WWII collapse.  What seems much more inexplicable is the steep dropoff in the later postwar period.