"He sings real good." Time was when teachers laboured valiantly to eliminate non-standard English forms altogether, but wisdom has prevailed.
Non-standard English is the normal speech of most of our population, so why not just accept it?
But writing (and other kinds of formal communication) are different - they need standard English. Conclusion: children should learn to write and speak standard English at school.
The two kinds of English are actually very similar, so there's not much to learn and most children pick up the main points unaided. However, some don't, and even those who do may find some guidance helpful. The Key Stage 3 Framework puts it like this: "pupils should understand the main differences between standard English and dialectal variations".
Take the non-standard pattern in: "He sings real good." How can we best understand the difference between this and its standard equivalent: "He sings really well"? Some people think non-standard forms are "mistakes", but they can't be mistakes if they're used all the time.
In class Discuss what makes the difference between standard and non-standard grammar. The answer is quite simple and builds on two grammatical terms: adjective and adverb. Explore this. You could find all the adverbs in a piece of writing and ask the class whether they would use them when speaking to each other and when writing. Here's the nub of the answer that should emerge from the discussion.
Standard English has a large number of adverbs that are closely related to adjectives. Usually the adverb consists of the adjective plus the suffix ly: "really", "slowly", "freely", and so on - there are hundreds of examples. The adjective and adverb pairs have much the same meaning, so they're like twins in a word family. For example: "If your cycling is slow, then you're cycling slowly." "If your arrival was recent, then you arrived recently." Even with "good", which looks totally different from its twin "well", students can see this pattern of change: "If your writing is good, then you write well."
A handful of adverbs do look just like their twins - "late" and "early", for example, are identical twins.
In non-standard English all the twins are identical. Here, if your cycling is slow, you cycle slow. There's nothing illogical or odd about it - standard German and Dutch actually do work like this. But it's different from the standard English that you are teaching your students to use in their writing. It's one of the few things that they can't import from their ordinary speech into their writing.