It is one of the poorest parts of Europe, and Communist governments tended to be big on a lot of things they couldn't deliver.

Communist governments delivered on that one.

Take a look here, specifically pages 21 and 23. The secondary education in Eastern Europe was more prevalent than in Mediterranean countries and Great Britain + Ireland (but less than in Nordic countries and Central Europe). And Czechoslovakia was one of the better Eastern European countries.

If you're comparing within an Indian population

I went and looked at the Jammu & Kashmir study and it is more convincing than the Czechoslovak study. Hm. It seems my scepticism about the 20+ IQ points drop was unfounded, <screech of rusty metal> changing my mind... </screech of rusty metal> :-)

But why did my intuition didn't like the large magnitude of IQ drop? I think because it implies that intelligence is very fragile and very easy to genetically screw up. But if the IQ drop is valid, then intelligence is very fragile. Hmm...