The below are my notes on “Doing Interviews” by Kvale.

Interviewer: You mentioned previously something about grades, would you please try and say more about that?
Pupil: Grades are often unjust because very often—very often—they are only a measure of how much you talk, and how much you agree with the teacher's opinion. For instance, I may state an opinion on the basis of a tested ideology, and which is against the teacher's ideology. The teacher will then, because it is against his ideology, which he finds to be the best one, of course say that what he is saying is right and what I am saying is wrong.
Interviewer: How should that influence the grade?
Pupil: Well, because he would then think that I was an idiot—who comes up with the wrong answers.
Interviewer: Is this not only your postulate?
Pupil: No, there are lots of concrete examples.

In response to an open question from the interviewer, the pupil describes their experience about grades. As Kvale notes, “the interviewer follows up on the answers, asks for specifics, and tests the strength of the pupil's belief through counter-questions.” Note the difference from everyday conversations; the interviewer asks, but does not answer.

The following interview is from an interview project by Bourdieu and his co-workers on the situation of immigrants and the poor in France.

Interviewer: You were telling me that it wasn't much fun around here, why? What is it, your job, your leisure time?
Francois: Yeah, both work and leisure. Even in this neighborhood there is nothing much.
Ali: There's no leisure activities.
Francois: We have this leisure center but the neighbors complain.
Ali: They're not very nice, that's true.
Interviewer: Why do they complain, because they…
Francois: Because we hang around the public garden, and in the evening here is nothing in our project, we have to go in the hallways when it's too cold outside. And when there's too much noise and stuff, they call the cops. (…)
Interviewer: You are not telling me the whole story…
Ali: We are always getting assaulted in our project; just yesterday we got some tear gas thrown at us, really, by a guy in our apartment. A bodybuilder. A pumper.
Interviewer: Why, what were you doing, bugging him?
Francois: No, when we are in the entryway he lives just above, when we are in the hall we talk, sometimes we shout.
Interviewer: But that took place during the daytime, at night?
Francois: No, just in the evening.
Interviewer: Late?
Francois: Late, around 10, 11 o'clock.
Interviewer: Well you know, he's got the right to snooze. The tear gas is a bit much but if you got on his nerves all night, you can see where he's coming from, right?
Ali: Yeah, but he could just come down and say. (…)
Interviewer: Yes, sure, he could come down and merely say 'go somewhere else.' (…)
Ali: Instead of tear gas.

Bourdieu et al. (1999 pp. 64-5)

In the above example as well, the interviewer follows up on the interviewee's answers, and seeks to clarify the interviewee's life world. Like in the first example, the interviewer challenges the interviewee's description of themselves as victims of harassment, and in contrast to the first example, the interviewees weaken their position.

Kvale offers the following advice on how to choose the proper number of interviews:

To the common question about interview inquiries, 'How many interview subjects do I need?', the answer is simply: 'Interview as many subjects as necessary to find out what you need to know.'

Thankfully, some more specific advice follows:

The number of subjects necessary depends on the purpose of the study.
If the aim is to understand the world as experienced by one specific person, say in a biographical interview, then one subject is sufficient.
If the intention is to explore and describe in detail the attitudes of boys and girls towards grades, new interviews might be **conducted until a point of saturation, where further interviews yield little new knowledge.

(Emphasis mine.)