One in ten students in my school is / are rich.

Unless your school has exactly ten students, I think I'd go with "are".

There are about 800 students in my school.

One / is/ rich

(in ten students is an adjective phrase describing the one student)

PUNKEY is correct.

I don't think so. "one in ten students" is another way of saying "one tenth" or "10 percent", and in any population of students larger than ten, it's going to be more than one student. In the example the OP cited, it's around 80 students, and that would be the usual case, and that would seem to take a plural verb. You would generally say "Ten percent of the students are rich" and this case is similar. I suppose you COULD say "is", but you can also say "are", and I think I would if I ever had occasion to use the statistic. If you said "One student in ten is rich", your emphasis is on that one student. "One in ten students" looks more toward the group as a whole, i.e. it fits many students, rather than focussing on the one.

"Ten percent of the students are rich" certainly sounds natural, possibly because ten percent by itself is a group. One in ten is still singular, even though the meaning is the same as 'ten percent'.

I don't agree. The ratio of rich students to all students reduces to 1:10. This is expressed on words as "one in ten". One is a singular thing. The subject of the sentence is 1, so it takes a singular verb. Is.

One in ten students are rich.
Two in ten students are pretty.
Three in ten students smoke pot.

It's a special way, and the 'one' is as singular as any other one.

Hi Contrex

I don't agree. The ratio of rich students to all students reduces to 1:10. This is expressed on words as "one in ten". One is a singular thing. The subject of the sentence is 1, so it takes a singular verb. Is.

One in ten students are rich.
Two in ten students are pretty.
Three in ten students smoke pot.

I suppose the bold word should be 'is'.

There was a foolish error in my post!

This is what I intended to post...

Maybe your subconscious was telling you something different than your conscious mind about which was acceptable, contrex.

Yes, I know... I still feel that you should follow 'one in xxx' with 'is' for the sake of consistency. You wouldn't say 'one of the students in my school are rich', after all.

Of course not. "one of the students" refers to only one student. "One in ten of the students" refers to a whole bunch of students in any school of usual size.

Out of utter boredom, I made a small research.

"One in ten students is" - about 50,000 hits.

"One in ten students are" - about 105,000 hits.

Contrary to the nationalities of our two last posters here, most of the former results originate mainly from North America and the latter mainly from UK.

Many of the UK results originate from universities.

The New York Times seems to prefer the singular form...

One in 10 Belgians has attempted suicide

Nearly one in 10 homeowners with mortgages was at least one payment behind in the third quarter

About one of every three Americans inherits a tendency to produce a form of cholesterol that appears to be linked with an unusually high risk of heart disease

One in eight adults in New York City has diabetes

One in every six marketing executives is now introducing new products or new product lines

One in four girls ages 14 to 19 is infected with at least one of four common diseases

In North Dakota, one out of 10 men is a member of the Benevolent and Protective Order of Elks.

Only one out of 100 personal income tax returns is audited

nearly one out of 20 children covered by Medicaid is taking psychiatric drugs like Ritalin

One out of every six American high school students suffers from asthma

One out of every five local television news directors around the country
say their stations have declined to broadcast some news reports in the last year because of fears of possible lawsuits

About one in every five pregnancies in Australia ends in abortion

One in every four young adults, aged 18 to 24, in New Jersey are addicted to tobacco products

One in every five fatal car crashes in the United States each year involves a driver who does not have a valid license or whose license status is a mystery to law enforcement, a study released today says.

One in every five victims is a child under the age of 7

One in every 250 diet program clients loses weight in the long term

Well, there you go, Contrex. As Timur's research shows, it's because you and the NYT are covert Americophiles, and I'm a closet Anglophile. Bet you didn't know you were, did you?

I am about as far from being an Americophile as it is possible to be.

Yes, I know, that's your public face, and you do have to keep up the appearance. I fully understand about these things.

yes . . . and fits semantically.