In Just How Stupid Are We? Rick Shenkman notes that in the 1940, 60% of Americans had not finished 8th grade. Currently, most Americans have had some college education. Yet they score worse on simple civics tests, such as 'what is the difference between Republicans and Democrats?', or 'how many branches of government are in the US?'
In science, it is pretty bad too. Political scientist John Miller notes that american adults in general do not understand what molecules are (other than that they are really small). Fewer than a third can identify DNA as a key to heredity. One adult American in five thinks the Sun revolves around the Earth. In one very funny study, (A Private Universe) they asked students at Harvard's commencement why seasons occur. Most thought it was because the earth is closer to the sun in summer. Harvard grads.