Variety is a Good Thing in writing, and for good reason. If you continually recycle a small vocabulary and a limited range of grammatical constructions, you not only bore your readers but you give the impression - rightly or wrongly - that you haven't yet learned the tools of your trade.
But the emphasis that we place on variety has a downside - it can come into conflict with clarity and precision, which are Good Things too. Variety means, among other things, not repeating vocabulary items - not writing things like: "After we had walked to the shops, we walked to the library and then we walked home."
But clarity means selecting words carefully to fit the intended meaning, and how could you possibly express the meaning "walked" better than by using the verb "walked"? No other word has precisely this meaning, so you lose precision if you go for variety.
Where does this leave us? It means that we have to be very careful in recommending the use of synonyms to increase variety. Sometimes it works, and sometimes it doesn't.
What budding writers need is a frameworkof ideas for thinking about word meanings. If you like an academic flavour, they need a theory of synonymy, and a little bit of terminology might help.
Synonyms are defined in the National Literacy Strategy glossary as "words which have the same meaning as another word, or very similar", and the examples given are "wet" and "damp". However, there are three different kinds of similarity which are worth distinguishing: 1. Exact synonyms, which have exactly the same meaning but are typically different in some other way - eg, frockdress, lorrytruck, horsegee-gee, tryattempt.
2. Generalspecific pairs, which define a more general idea and a sub-case - eg, treeoak, gowalk.
3. Contrasting pairs, which are similar but distinct - eg oakash, marchamble, raindrizzle.
In the drive for variety, the only safe option is the generalspecific pair. For example, you can always replace "walked" by either "went" or "came" and, if it fits the facts, you may be able to replace it with something like "ambled" or "marched". Exact synonyms are problematic because they may (and often do) produce inconsistent "style"; to take an extreme example, a description of a horse-race is not improved by replacing "horse" by "gee-gee" or "steed" unless these fit the grand plan.
Contrasting pairs are even worse, because they change the meaning. Rain and drizzle are different, so it's simply inconsistent and confusing to replace one by the other. So the one thing not to tell the children is that they should use a thesaurus to avoid repetition. A thesaurus is a very crude tool indeed except in the hands of an expert.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk