selected Phd student did nothing for the first year

Question

What would be the fate of a CS PhD student in the US that wasn't able to implement something during the first year of their program? How the supervisors react to such students considering they selected them in the first place?

Answer 1

Normally the early part of a US doctoral program is coursework leading to the comprehensive exams. There are a few exceptions. And starting with a masters, instead of the usual bachelors, can be a bit different, though prelims are still facing most students. Most students (again with exceptions) don't have a "supervisor" this early. The system is very different from the European one and some others. Doctoral students, in particular, are normally admitted by a committee, not by an individual supervisor (again, some exceptions).

There is also the issue of what it means to "not implement" anything. Given the above typical case, that would be pretty common, though good grades in coursework is expected.

But in the case in which a student is in a particular lab, working for a particular supervisor, questions would be asked and answers expected. Nothing specific would automatically happen. Students are students, not accomplished researchers.

In addition, some problems given to students are harder than others. No "visible" accomplishment might be a result of a research problem that turns out to be harder than initially expected. There are no guarantees when true research is undertaken. Some problems take years to crack. Some have never been cracked yet (or maybe ever).

But a lazy student, one who doesn't try, is another issue. They might be given some warnings about their work ethic.

I don't think the situation you describe says much of anything about the selection process. People make mistakes. It happens. Students with seemingly good prospects can have things happen. Anything from "hitting a wall" to medical/emotional issues or family problems can disrupt even a good student. People aren't perfect, either faculty or students, so some undesirable things happen. The system tries to make the bad things happen infrequently.

See this for how the admissions process works in the US for some background.