The fact is that for many centuries Latin was the only language used in scholarly writing throughout Western Europe, so it continued to exert enormous influence even when scholars switched to their native languages, such as English. Isaac Newton did science in Latin, and it's only a generation since Oxbridge expected every undergraduate to be able to read Latin.
Not surprisingly, Latin patterns spilled over into English. A great deal of English syntax is modelled more or less directly on Latin but to modern writers this is simply a matter of history - interesting for some, but not essential for good writing.
However, some bits of Latin still exist in academic writing, and don't make any sense at all except in terms of Latin. These are cases where KS3 writers really do need to know something about the history of their language tools.
Perhaps the most obvious examples are Latin abbreviations, e.g. "e.g.". Why on earth do we write "e.g." when we mean "for example"? Why don't we just abbreviate the native phrase (as they do in German), giving "f.e."?
Well, the fact is that we don't, and that the established abbreviation is based on Latin - "exempli gratia", meaning "for the sake (gratia) of an example (exempli)". The etymology matters in this case because of a punctuation detail: the abbreviative full stops after the two letters, showing that each one was the first letter of a complete word.
Word-level punctuation is on the agenda for KS3 writers, and it includes the rules for using full stops. The simplest rule is that each stop stands for the missing bits of a single word. Thus we write just one stop in "Prof." or "E. Sussex". But "e.g." has two stops. Why? Because there are two words - "exempli" and "gratia". There are not that many Latin abbreviations, but they all belong in the toolkit of literacy. You'll find a short list on our web site at www.phon.ucl.ac.ukhomedickttaclick on wordpunc.
Apart from "e.g." they are: i.e. (id est), a.m. (ante meridiem), p.m. (post meridiem) and cf. (conferre). Notice how the last one only has one full stop, because it's based on a single word in Latin.
The point of this bit of grammar is to throw light on what would otherwise be an arbitrary and puzzling list. And it gives you a chance to discuss something much bigger: how the influence of Latin has made formal written English so different from casual speech.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk