It is easy to forget the bits around words - the spaces. Without them meaningbecomesdifficulttofollow. All teachers will have noticed that sometimes the spaces crop up or go missing unexpectedly. We see formations like "alot" and "thankyou", written as one word instead of two.
Sometimes pupils just have to learn case by case - "in fact" does have a space but "indeed" doesn't. But one very general principle that all key stage 3 writers should know is that the basic bricks of sentence structure are separated from each other by spaces (or by apostrophes). For instance, when we write "Maybe it will rain" (or "Maybe it'll rain") we separate four bricks - the adverb, the subject, the auxiliary verb and the full verb.
Pupils know and apply this principle.
But sometimes they write "may be" without the space in a sentence like "That maybe difficult". Teachers hate that. If "will rain" needs a space between the auxiliary verb and the full verb, then so does "may be".
Suppose you reveal this truth to a KS3 class and they look blank. The chances are they don't see the difference between this "maybe" and the legitimate one in "Maybe it'll rain." They've learned to write "maybe" as one word, so they always do. Reasonably good phonics (though they actually sound slightly different), but bad grammar; good enough at KS2, but not at KS3.
As a starter activity, get pupils to look for alternatives. Begin with the adverb "maybe", as in "Maybe it'll rain". Write this sentence on the board with space below "maybe". What single words could replace "maybe"? Expect a list including "perhaps" and a few others such as "tomorrow" and "soon". Now try to replace "may" and "be" separately in this sentence and see how hard it is. Even "can" doesn't work instead of "may" ("Can be it'll rain"), and no other verb can replace "be" - not even the best candidate, "happen" ("May happen it'll rain"). This "maybe" is a brick that pupils can't divide any further, even though they can see that it's made up of "may" and "be".
Now look at the offending example: "That maybe difficult." Write the sentence up with plenty of space under "maybe" to list the single words that can replace "may" and "be" separately. Instead of "may" pupils could use "will", "can" and a number of others, and instead of "be" they might use "become" or "seem". In this sentence, "may" and "be" don't form a single indivisible brick, but are two juxtaposed bricks. Word space deserves so much attention because it plays a part in a sentence's meaning.