they, their, them, ahem . . . (or very well, consider this . . .)

Singular/plural mismatches between subject and pronoun can be avoided, and in most cases, effortlessly and naturally.

Here are some examples:

When a teacher gives timely feedback, their students benefit.

Ask everyone what toppings they want on their ice cream sundaes.

If your child asks for a present from Santa, you will you try your hardest to get it for them.

Notice that teacher, everyone, and child are singular subjects.  Notice that their, they, and them are plural pronouns.

This phenomenon is ubiquitous.  I don't consider it correct because it is common any more than yelling at kids is correct because it is common.  I also consider it inoffensive (unlike yelling at kids), so why bring it up?  Because at the technical  but not arcane level, this is not a logical match and some people will be distracted by it.  When we write, we want our message and writing to flow without interruptions for maximum impact. (You may question:  what if I don't care about the impact of my writing?  Well, that's a discussion for another day.)

So here's an easy variation:  make the subject plural:

When teachers give timely feedback, their students benefit.

Ask all the guests what toppings they want on their ice cream sundaes.

If children ask for presents from Santa, adults try their hardest to get them for them.

Now a final word about writing rules.  The British essayist and novelist George Orwell said, after giving a list of five writing rules, gave a sixth rule which I apply to all writing rules I share with you:

Break any of these rules sooner than say anything outright barbarous.