On the contrary, it is needed in standard English.

Does this answer your question? Why is there no article for "president" in this sentence? Also Why is there no article for "president" in this sentence? and Serve as (the) chairman and Is it correct to say (They elected him as a chairman)?, among others.

@FumbleFingers to be elected president (no article) is not the same as to be the principal of a school.

@Lambie: We have principles, but not principals in the UK. But there are headmasters both sides of the pond , and according to this chart, until very recently most writers didn't include the article there. The syntax of the referent is the same regardless of whether it's someone being elected [to a position] or someone who is [holder of the role / title].

@FumbleFingers so we can say both sentences with or without 'the' are correct. It's not mandatory to drop the 'the'.

@FumbleFingers I never do that to you for minor vocabulary points. That is irrelevant in any case. I would not use: He is headmaster of the school. I would use: He is headmaster of a school.

@Lambie it's a question of my exam. Options are 'the' or no article. I have chance to challenge my examiner. If both the options are right then we all will get the mark for this question.

I have the luck to challenge my examiner. Both options can be right. Context is everything.

@ArindamBiswas: It's good that you can "challenge" the examiner. See the chart linked to in my second comment, (for "headmaster", but syntactically speaking "principal" is the same; it's just not used much in British English). The chart clearly shows not only that the article is optional - it's also obvious that historically it wasn't usually included (but according to the chart, both versions are now equally likely). People can argue about whether the usage shift now represents some kind of shift in meaning (unlikely, imho), but clearly both versions are / have been used extensively.

@FumbleFingers Thank you. Now I got my answer!

Thank you @Lambie. English is not my native language. So please overlook my crude english.

Crude is not a word I would use to describe it. :)

@FumbleFingers - "The Education Outlook, Volumes 70-72 (1919), p. 29: Mr. R. B. Henderson , headmaster of the Strand School, Brixton Hill, has been appointed headmaster of Alleyn's School, Dulwich.". My old school, but much later!

@FumbleFingers I work at a school in which the lead teacher is styled "Principal". Whether the lead is "Headteacher" or some other term (Provost for example) is a matter for the school, not the dialect.

@JamesK: I was surprised to see that according to [this BrE-specific NGram,]() school principal overtook schoolheadmaster back in the 50s. But this AmE-specific chart shows the latter is so uncommon in AmE that I'm guessing most of the data contributing to school principal in the BrE chart are just misclassified AmE texts anyway. The usage split is real, regardless of any individual establishment's choice

I meant this BrE-specific NGram.

...I see the lead teacher is starting to gain traction against the head teacher in AmE, but as this BrE chart shows, it's still very uncommon in BrE. Your usage clearly favours the American style, and it's not really the establishment's choice.

I just checked my field. I was once the chief programmer, but if I was still working today, apparently I'd be the lead programmer. I still remember when the dozen or so programmers in that department were issued corporate business cards where we all changed from "programmers" to "consultants". What's in a name, huh?

I think a British person talking about an America car would use "boot", but a British person talking about the lead teacher of an American School would use "Principal". That's the subtle distinction I'm making. Similarly my school chose "Principal" in part to mark it as different from other schools.

oic. Yeah - I'd refer to the principal of South Park rather than the headmaster. But to me that's on a par with calling snooker ace Ronnie O'Sullivan by his preferred handle, even if I know lots of other Ronalds who all style themselves Ron. People get to choose their own names most of the time (I've seen the Donald often enough, but never Donnie Trump! :).

Don't (or didn't) some very 'tony' New England boys' schools have headmasters? And buildings like Rugby or Eton? [Update] Groton School is a private college-preparatory day and boarding school located in Groton, Massachusetts. It is affiliated with the Episcopalian tradition. [...] the current Headmaster [is] the South African-American Temba Maqubela (2013–present).

Eton, one will be aware, has a 'Head Master' (two words, both capitalised).