Besides the factors above about lack of work and inability to study as well as semi-illiteracy, I found that some students were just too damn stupid to grasp the material. I taught one fellow who was very eager to learn and pass the course (foreign language), but he started failing early in the course. I tutored him twice a week during office hours and found he was unable to understand the most simple concepts no matter how many ways I explained them.
I later taught in a college in which I was provided the IQs of all the students. Not surprisingly their grades tracked fairly close to their IQ scores.
Declining literacy and numeracy are widespread. I taught high school science for 7 years before retiring. I was appalled at the amount of cheating, poor basic skills and lack of knowledge of most of the youngsters. They were in a suburban parochial school. The long-time teachers there told me that they saw a huge drop-off in student learning when mobile phones became prevalent among youngsters. Most of them lost focus and discipline around that time. They also read very few books, which require more sustained concentration. Technology has its advantages, but it is also harmful to young people in many ways.
Chrome offered to translate your FR home page.
Pascal - two thumbs up!
There was a reason why students took the SAT and colleges used to have minimum scores for acceptance.
I once was paid to tutor a young woman in a relatively easy subject like history or sociology. After a number of sessions I realized that she was pedaling as hard as she could but did not have the baseline abstract thinking abilities to comprehend and process the information.
We discussed her interest in hairdressing. A fine concrete skill. And she pursued it.
There are many concrete thinkers who excel in their areas of expertise.