Sociolinguists have been fighting dialect prejudice since the 1960s, but negative and uninformed views about non-standard English are regaining currency in media and educational debates. Most recently, Carol Walker, headteacher of a Teesside primary school, wrote a letter to parents asking that they help tackle the "problem" posed by their children's use of local dialect by correcting certain words, phrases and pronunciations associated with Teesside (including "gizit ere" and "yous").

Naturally, I support the school's aim of teaching pupils to use written standard English so that they can progress in future education and employment. However, focusing on speech will not improve their writing. There are three reasons why the methods advocated in this letter are unhelpful and damaging.

First, the letter seems to assume that to teach standard English it is necessary to erase features of the local dialect. As a native of Teesside, I recognise several of the so-called "problem" words and phrases. I still use them, as well as standard English; they're part of the repertoire of linguistic forms and meanings I and, as my academic research shows, primary school children in Teesside draw upon.

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For example, like me, the children I worked with sometimes used the banned "gizit". This is a condensed form of "give us it" (it's a normal process in informal speech that when talk speeds up sounds get left out). The use of the plural pronoun "us" instead of singular "me" is common not only in Teesside but in dialects across the English-speaking world, making a command less demanding. The letter states that children should say, "Please give me it" as an alternative, but such commands are quite risky, since they can sound impolite.

I find children use "give us it" with friends as a way of softening the command, by appealing to group solidarity. The same children use "give me it" and other "standard" alternatives such as "Can I have it?" and "I need it". It depended on context. Clearly, they had command of both standard and non-standard forms, using them discerningly.

Second, the letter is wrong on a number of points. It says that children should not say "yous" because "you is NEVER plural". This is simply incorrect: "you" is used for both second person singular and plural in standard English, but historically, "you" was the plural form while "thou" was singular. Many languages still differentiate between second person singular and plural (e.g. tu and vous in French). Standard English no longer makes this distinction, but many dialects of English, including Teesside, Newcastle and Liverpool, as well as Irish English, use "yous" to fill the gap. US English has also developed similar strategies, using forms such as "y'all" and "yinz" for second person plural.

Finally, and perhaps most importantly, to learn and develop, children must participate actively in classroom discussion; they must think out loud, answer and ask questions, and challenge each other's and their teachers' ideas. When teachers focus exclusively on the form of this talk rather than the substance, children may simply remain silent in order to avoid the shame of speaking "incorrectly", and miss the interactions crucial to learning.

Ultimately, it is not the presence or absence of non-standard forms in children's speech that raise educational issues; rather, picking on non-standard voices risks marginalising some children, and may make them less confident at school. Silencing pupils' voices, even with the best intentions, is just not acceptable.

Dr Julia Snell lectures in Socio-linguistics at King's College, London; www.snell.me.uk; twitter.com/@SnellJulia