I knew abstractly about the difference somewhere around third or fourth grade, had more trouble pointing to Romania, because I didn't know about anything much from there, Poland on the other hand was a lot clearer because I had a buddy whose dad was from Poland and he would take occasional trips there in the couple of years before the fall of the soviet union, and tell me about all the churches everywhere that weren't supposed to be there. It was easier to find on an unlabled map because it is on Germany's eastern border, and we all know what happened there! So, probably early in middle school is when I learned about the two. What really stayed hidden until the end of the Soviet Union were all the places like Kyrgyzstan, Tajikistan, Belarus, and Kazakhstan! Suddenly all these places popped out of nowhere, on most maps it was just a big green blob labeled, "Soviet Union" or "Union of Soviet Socialist Republics" If it was labeled like the latter, then if it was detailed enough, you might see names like "Tajik S.S.R." and "Kazakh S.S.R."