Students often struggle in college -- it is certainly the case that many students arrive in college unprepared. But having reflected on the last several years (in which this problem has been particularly apparent), it's clear that the difficulties students are having have nothing to do with ability to handle the material. So what is preventing most students from doing well in college? In my experience, many problems, not all but surprisingly many, would be resolved if students were better at dealing with three things.
(1) Percentages. To someone who has never experienced it, it is difficult to convey how exhausting it is to have to explain, to yet another student, and sometimes multiple times, that an assignment worth 25% of the final grade is more important than an assignment worth 5%. I once had a student who sheepishly told him that he almost dropped the class after doing badly on an assignment until his girlfriend, who I think was a math major, insisted that they sit down first and see exactly how badly he was doing in the class, after which she turned to him and said, "Idiot! You were going to drop the class because you currently have a B+ in it!" This problem has only grown worse over the years. In a sense, it's not merely a matter of percentages; it's a matter of priorities, which just often happen to be percentage-related due to the make-up of the final grade. Students do better who develop habits of worrying about what is more worth worrying about, and worrying less about what is less worthy of worry.
(2) Citations. I get many students who simply do not understand how to do basic citations. They will sometimes not know at all how to do footnotes or endnotes; they will often incorrectly think that they have cited a source if they have just listed it in the bibliography; and (more understandably, but still common) they will think they only need to cite if they directly quote. Every college student should have at least basic familiarity with at least one major citation format -- it doesn't matter which. If you have a professor who is a stickler for citation format, you can easily adapt to their requirements, if you already know the basics of at least one format; if you have a professor who is fairly easygoing about citations, any one will do. Citation not only is used for giving credit to sources, it is also a form of evidence (they contribute to showing that your claims about a source have a foundation in the text), and it (at present, at least) provides evidence that you did the work yourself. Citation is not an end-all or be-all; it is a means, and not an end itself; how important it is varies considerably. But many students would do much better on some important assignments if their citation practice were even a little better.
(3) Deadlines. One of the very noticeable things these days is that many students lack any habits for dealing with deadlines. Indeed, it seems custom has tipped the opposite way -- they have developed the assumption that all deadlines are negotiable. In college this is still not so. Instructors may be more or less strict about due dates for particular assignments, but they certainly have their own deadlines for their courses (which is sometimes a reason why they are strict about particular due dates), and some of these deadlines have legal weight. Constantly having to grade straggling papers significantly increases the burden of a course for an instructor -- in providing feedback, in being timely in grading, in keeping track of assignments, and more. Instructors like myself may be willing to bear some of that increased burden, but there is a point beyond which it becomes simply unmanageable, and as more and more students try to get extensions or turn in late assignments for increasingly less serious reasons, a stricter policy becomes more and more attractive. One of the reasons to worry about a more generous policy here is that an increasing number of students lag farther and farther behind as the course continues, until they completely crash and burn. And, of course, as life always runs out of a time, a course always runs out of time; one advantage of a course over life in general, is that you know beforehand when the course is going to end. Everyone procrastinates on some things; but we are not even talking about procrastination here. We're talking about recognizing deadlines as deadlines and treating them as such. Cramming is less than ideal, but it has the great benefit of taking deadlines seriously; many students are so bad at the latter that they would do better even if all they were doing was more cramming.