Number words - with pronouns
Be careful about whether you use singular or plural pronouns with the third person. You may hear a message on the phone "The caller withheld their number." How many callers were there? Logically - academically - it is clearly better to use a singular pronoun such as "his". But then we are making a sexist assumption: to avoid sexist language, we could say "his or her". (There is a case for preferring "her or his", because this way round the pronouns are in alphabetical order and we counter the sexist assumption that masculine precedes feminine.)
Whichever way round you say the two pronouns 'his' and 'her', it feels clumsy, so in natural spoken English, the word "they" may be used instead - following a singular noun..
But this is wrong, in formal English.
Our advice is to use plural nouns wherever possible in academic English. Then you can use they naturally and easily, and certainly more fluently. "Students who exceed their word-count limit ... " is more natural than "A student who exceeds her or his word-count limit ... ".