>>>My former manager once told me, that two most common mistakes native speakers do are "it's/its" wrong usage and using word "irregardless" <g>
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>>>I noiticed recently that my son's teacher spelled "yogurt" wrongly in the paper distributed to homes...
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>>My friend's daughter (back home) wrote "helihopter" in her homework. Parents noticed, and she almost burst into tears: "I know, it's helikopter, but I must write it like this because teacher does so".
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>Probably due to the teacher's accent? and the e european "C-H" pronunciation/approixmation to western "K"?

Not even close. H is just slightly more aspired than the English h (as in "him", not in the thousand places where h is not a h), and k exactly the same as in English.

And "because teacher does so" means "teacher writes it so". And pronounces as well - we're phonetic, remember?

It's the illiteracy. Equalization by similarity - just as some people would say name "x and y" as "iks i iksilon" instead of "iks i ipsilon", or would call messrs. Laurel and Hardy "Stanlio & Olio". And they'd never notice any error in their ways.