Your KS3 class would probably be rather surprised, but all the alternatives are either things they already say, or things they should be learning to write.
Suppose we say to you that reading softens the brain and you were inclined to deny it. How could you do it?
The main options for denial use words like "not", "never" and "no":
"Reading doesn't soften the brain"; "Reading never softens the brain"; "No reading softens the brain". (Nice ambiguity in the last example!) As you are no doubt aware, the grammar of these words is actually rather complicated (for example, just think of "isn't reading" and "doesn't read", or "not reading" and "no reading"); but the good news is that every native speaker is an expert and needs no help with these details. The same can't of course be said for English as an Additional Language learners, so they may need a bit of guidance.
However, there are other options which are worth exploring with the class as a way of deepening their understanding of how their ordinary language works as well as of expanding their repertoire in writing.
In speaking you could say (or shout) "No!" This is a very useful little word because it packs so much meaning into so little sound by making the hearer provide most of the meaning: it means "Not that", but doesn't tell the hearer what "that" is.
When we hear "no" (or "yes"), we have to find some sentence-sized idea that it could relate to. This could be what we have just said ("Reading softens the brain" - "No!"), but it could just as easily be an action that we're about to perform (you see one of us about to jump to our death - "No!").
The impressive versatility of "no" is matched by the danger of misunderstanding, so we often end up combining "no" with "not": "No, reading doesn't soften the brain", or "No, don't jump!". This may seem redundant, but it's actually sensible - "no" gives a very fast summary, while the full sentence removes ambiguity.
In writing you find a pattern which hardly exists in ordinary speech, and which is a point of growth for more ambitious KS3 writers: "In no sense does reading soften the brain". The pattern generally starts with a negative word or phrase (in no sense), and then switches the verb and its subject just as in a question. It does exist in ordinary speech (So am I - Nor did we - No way am I going to apologise first!) - but writing expands the list: "Hardly had he ...", "At no time did she ...", "Not only were they ...", "Never did I ...". Nowhere in speech will you ever find examples like these.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk