This is written by Geoffrey K. Pullum, professor of general linguistics in the School of Philosophy, Psychology and Language Sciences at the University of Edinburgh.
The real tragedy is that the whole notion of "subordinating conjunctions" is bunkum: there's no defensible category of words that includes the ones that traditional grammar gathered together under that heading.
The government is not just foisting the learning of grammar terminology on children; it is foisting on children (and teachers) the task of learning BAD grammatical terminology that does not comport with any sensible analysis of the language. I wish I knew how to get this across to the benighted people in question: they are not just dragging schoolchildren's grammar education not just back to the 1950s (which might or might not have a few arguments in its favour) but dragging it back to something more like the 1750s. Even according to the goals and principles of the traditional grammarians themselves, their analysis is painfully inadequate, in fact dumb. The reasons were pointed out not only by The Cambridge Grammar of the English Language in 2002, but by various generative grammarians in the 1970s, and by Otto Jespersen in the 1920s, and even earlier --- particularly in a paper by Professor John Hunter published in the Royal Society of Edinburgh's proceedings in 1784!
It isn't too difficult or technical to explain the reasoning (I tried to present the arguments simply in a Lingua Franca post at http://chronicle.com/blogs/linguafranca/2015/11/08/prepositions-as-conjunctions-whales-as-fish/). The traditional account posits a class of "subordinating conjunctions" that includes (among others) words like "after", "although", "because", "before", "for", "if", "lest", "since", "that", "though", and "whether". But "that" (as in "I doubt that he did") and "whether" (as in "I doubt whether he did") are just meaningless markers of subordination: "that" signals the beginning of a declarative subordinate clause while "whether" signals the beginning of a closed interrogative subordinate clause. Words like "after", "because", "before", and so on are totally different: they are fully meaningful items that function as heads of phrases --- they are in fact prepositions. (Yes, prepositions. Some prepositions can be followed by clauses rather than nouns or noun phrases.) As Hunter pointed out in 1784, this should be very clear in the case of words like "after": it is surely the same word that we see in "I can't do that until after our meeting" as we see in the virtually synonymous "I can't do that until after we meet." Traditional grammar (like all published dictionaries) makes "after" out to be three different words. Likewise "since": it has to be a preposition in "I've liked her ever since our first meeting"; a 'subordinating conjunction' in "I've liked her ever since we first met"; and an adverb in "I've liked her ever since." Madness. Surely, as anyone can see, it's one word, with one meaning. Look up "since" in any dictionary: they make it three words, tagged as "prep", "conj", and "adv"! The tradition of English grammar is simply making a mistake, rather like taking male and female blackbirds to be different species because the female is brown. And if the government is going to meddle in the details of language education in the 21st century, and issue tests of grammar vocabulary that they want children to be able to pass, they ought to have some conception of what's been discovered about language during the 18th, 19th, and 20th centuries. --
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