Do "foreigners" score lower on U.S. Intelligence tests? They do when poor English language skills intrude. When the requisite language skills are present the differences either disappear or reverse. Why reverse? Because the general motivational level and academic performance of U.S. students has been declining in comparison to students in other countries.
You can blame it on poor teaching or on passive learning. My experience, after 35 years teaching at baccalaureate and graduate levels is that the majority of all students, both domestic and foreign, are passive learners. They don't engage the material, they either ignore it or simply memorize it. And they often argue their unformed opinions against any information that disturbs their status quo. My guess from your posts in this thread is that the previous sentence describes you.
I made it a point to start most courses with the statement "I'm not here to indoctrinate you, I'm here to give you objective information and some interpretations of that information, that will give you the opportunity to make rational judgements on your own."
This is getting long so I'll close by saying that in 35 years of teaching I never observed as general truth the complaints you raise . Your perceptions are based on very limited personal observation. Students appear to be bright, or not bright, based on their desire to receive new ideas and process them. Those who work actively at that endeavor seem bright; those who remain passive or refuse to consider any new ideas seem less bright. Neither race, nor place of origin, nor citizenship, nor native language provide any predictive value for determing "intelligence" or learning aptitude.
To suggest otherwise seems to me to demonstrate advanced xenophobia.
IQ tests used to screen students have math based portions, which again, are heavily correlated with what would be found if their vocabulary size in their native language, was to be measured. Of course I am not implying that students who don't speak English should be gauged by their English vocabulary size.
It's my guess that your perceived trend in American students would probably best be understood by considering other differences between American and foreign students that have nothing to do with motivation. There is no longer any reason whatsoever for students to be dependent on professors for information on the subjects in their field. Access to information far beyond what the average college professor is familiar with is readily available to anyone with a search engine and the brains to compose information from different sources.
What you may perceive as "poor motivation" may in fact be the exact opposite. When you consider that by comparison many foreign students are here for economic reasons (and thus are not motivated to do more than they have to impress their professors) and are financially dependent on the department for their livelihood the situation becomes much clearer. Also, as a place where many cultures have clashed in a battle to coexist, individualism is far more accepted here than it is in most of the places our foreign students come from. This is both true in the sense that some of their governments suppress independent thought, as well in the sense that less diverse environments inhibit social maturity. (How do you react to someone who's behavior you don't understand or accept?)
Lets do a thought experiment for a second here. Imagine hypothetically you had an American student of extreme intelligence, analytical skills, and motivation to learn. He was financially secure and as such his motivation for being involved in academia was pure (for the pursuit of knowledge) and thus not social in nature. As this was his nature, he frequently sought information of interest to him long before he even became involved. Perhaps by the time he arrived in your class, he had amassed an enormous amount of knowledge from many different disciplines and organized them into seamless formal models. All these things being the case, 90% of what you presented in your class was already well understood by him - both because his analytical skills allowed him to recognize many of the concepts as instances of more general ideas he had seen in many other disciplines, and because he had already investigated the area on his own.
How do you think such a student would superficially seem to you? I personally, despite immediately knowing the correct answer to just about every question ever asked in a class (and often a formal proof of how the professor made an unfounded assumption in how he asked or answered the question), do not respond to questions unless no one else knows the answer. I do this so that lower IQ students do not lose motivation to participate.
In classes where I do end up answering a large percentage of the questions because the material is actually conceptually difficult enough to prevent most of the students from commenting, the professors begin to actively combat the resulting perception by making ridiculous straw man attacks on my statements or just obviously wrong counter-claims and then just forcibly denying any response. Based on their body-language both in these situations and in similar one-on-one situations their behavior is clearly driven by deep-seated emotional insecurities towards intelligent white people.
Some of these professors even try to extend this attitude into the grading, where open ended short answer questions suddenly become more specific during grading in such a manner that all favored students conveniently meet the new criteria. Or where a professor arrogantly ignores a path of argument, which could be objectively proven (and was on the paper had the professor actually read it) that isn't a strict regurgitation of simple minded concepts presented by him in class.
And presentations are hilarious. Imagine a professor who has been teaching the same material for 20 years, only minimally able to understand ancient prototypes of modern methods trying to make sense of a student referring to or presenting a novel contribution to cutting edge research he had gained access to through paid subscriptions to journals that weren't available in the universities collection, which the professor didn't use anyways. In my case the professor tried to participate despite his ignorance by asking completely irrelevant questions that might have made sense if directed towards the aforementioned ancient prototypes. Then the professor proceeded to give me a bad grade, which he couldn't justify when faced with a Socratic method like questioning ("So what do you think I could do to improve?") except for to say that a truck driver could have presented the same material. The material covered was the topic of several courses in the same university, and I had condensed the most important points into a 45 minute lecture which everyone completely understood the ideas. This is in addition to several novel idea presented that would help deal with current issues and were the topic of my research (he became very defensive in response to the idea when presented). What way left is there to criticize the presenter other than to naively imply that the material was easy to begin with and that is why it seemed simple when I presented it.
Then he went on to praise another student of his own culture who had simply presented a simple minded use (uncontrolled experiment of limited use even if had been done correctly) of tools provided in another class and passed them off as his own creation after changing a few lines in the open source code.
So to summarize:
1) I don't participate to capacity in class because when I do, the professor has an emotional breakdown as does half the class. The guy who sits in the front of class and repeats everything you say in the form of a question is demonstrably and objectively a mongoloid idiot by comparison. Of course any demonstration of this other than the difference in GRE scores is avoided because that person desperately avoids any confrontation with me despite trying to downplay my abilities in my absence.
2) The professor doesn't understand ideas I present to him, not because they aren't well presented but because they are complex and he would rather assume American students like me are stupid than take the time to follow the logic. (And probably because what is a simple logical step to me is much harder for him to follow.)
3) Also, I am not going to be amazed at the way the simple minded project the professor gave me turns out. I already logically deduced exactly how it would turn out 30 seconds after the project was assigned. I am not going to test 20 different parameter values and giddily show the results - I am much more likely to give a proof of how all those attempts would come out the same way.
4) Yes I am aware that you are that you are leeching off of my hundreds of thousands of tax dollars to fund your perverted racial fantasies in which American students are less intelligent than you. Yes I am going to raise awareness and put a stop to it.
So yeah, I propose that the above mentioned student is the exact student you would ineptly or perhaps selfishly describe as "lacking motivation".
Anyone who is actually affected by your statement that "I'm not here to indoctrinate you, I'm here to give you objective information and some interpretations of that information, that will give you the opportunity to make rational judgements on your own." is not that bright. To make such a statement shows that you don't understand where a counter claim to it would come from. No professor THINKS they are indoctrinating students, they all think they are being objective. That's just what they ARE doing when they straw man all arguments in opposition to their own beliefs from sources they don't like.