3. grammatical sophistication is required: Effective error sheet work requires not only a respect for grammar, it also requires grammatical knowledge and grammatical skill. In the first place, teachers using this method should have a fairly deep understanding of fundamental grammatical concepts. To illustrate this with an example: one of the most common, and most serious, errors ESL instructors have to deal with is faulty sentence punctuation. Correcting this mistake, in a superficial way, is a simple matter: in the case of a “run-on,” a matter of inserting a period, and perhaps removing a comma; in the case of a “fragment,” a matter of removing a period and perhaps inserting a comma. When this sort of error appears on an error sheet, however, that sort of correction may not be enough. It may be necessary — and it certainly will be necessary on occasion — to give a real explanation of why the error is an error. Such an explanation will almost certainly require a reference to the concept of a clause, a concept which can be properly understood only by contrast to the concepts of a sentence and a phrase... Moreover, in many cases a really satisfactory explanation of a punctuation error — one which will enable a student who habitually makes mistakes of this kind to detect and eliminate them — will often require reference to the distinction between finite and non-finite clauses.
The second way in which the use of the error detection method requires grammatical knowledge is this: to use error sheets effectively a teacher has to have not only a solid understanding of fundamental grammatical concepts but also the skill of applying that knowledge to a wide range of instances. The items on an error sheet do not come pre-processed and neatly labelled as do the items in a conventional grammar text. (And of course the fact that they do not is crucial to their value as error detection practice.) The fourth item in Error Sheet 1 — “A woman named Brenda. She charged murder” — can be taken as an example the need for skillful application of grammatical knowledge. Here the fact that the phrase, “a woman named Brenda,” is a fragment would be obvious to any teacher, as would the fact that the mistake could be corrected by inserting a period. However even a teacher who was theoretically familiar with the idea of a prepositional verb could easily miss the fact that that concept was the key to correcting and explaining the second obvious mistake in the item. Moreover, even a teacher who was theoretically familiar with the idea of a reduced adjective clause could easily fail to notice that the fragment contains such a clause and to point out to his or her students how the use of such an element can contribute to punctuation mistakes. (For example, a more sophisticated teacher might, if it seemed appropriate, point out that the fragment could, even though absurdly, be interpreted as a grammatical sentence.)