A colleague of mine has a very weak student in class and she's worried that he might fail his final English exam, which he's taking in May. Now and then, during our regular coffee chats, she comes up with a little rant. Last time she looked really frustrated when she told me that the student, who should by now be somewhere around the B1-B2 level, can't use basic grammatical structures correctly. I should stress that my friend does her best to help this particular student and she has spent lots of extra hours with him after school explaining stuff.
Nevertheless, she is desperate that, for example, the student uses the present simple tense when talking about past events. So instead of saying: The other day I went to Prague ... he says: The other day I go to Prague .... I couldn't but agree that this could be a real problem during his state exam, but then I thought of the last conference I went to, and I remembered Piotr Steinbrich's plenary speech, in which he mentioned the fact that although the present simple is considered one of the most basic grammatical structures, i.e. A1 structures as described by CEFR, it can actually indicate a fairly advanced level of English when it's used for talking about past events. So in an attempt to console my friend, I told her humorously that during the actual exam we can pretend that the student uses the structures on purpose.
My colleague smiled faintly but immediately went on to tell me another example of the student's ignorance. "Just imagine, I asked him something about dinner and he started describing his typical lunch at the school canteen. I couldn't believe my ears!" I sympathised with her but then I remembered another conference, particularly Nikki Fořtová's workshop, during which she talked about differences in lexis across various cultures. She told us, for example, that *pond* is not what Czech people think it is and that *dinner* may actually be *lunch* in a particular cultural context. So again, I tried to lift my friend's spirits by telling her that if this happens, we can pretend that the boy is actually on topic.
Now, this chat I had with my friend got me thinking. We have all sorts of errors, such as typos, slips of the tongue, errors related to interlanguage, random errors, systematic errors, etc. But sometimes students use structures which may be correct under certain circumstances but as their regular teacher you know that they use them because they can't use the ones you expect them to use. I mean, the student mentioned above does not know that dinner may be lunch or that present simple can be used for past events. He simply messes things up and his teacher knows it because otherwise he makes mistakes which imply that his level is not that high. The question is whether and/or how to penalise those errors in disguise.
I face a similar dilemma when teaching reported speech or the past perfect tense. The rules are not always clear-cut and as a fairly advanced user of English I know that it's not always necessary or even desirable to use a more complex structure, simply because it's not natural.
The obvious conclusion is that as long as the student is understood, everything's fine. On the other hand, our students are required to take exams which are designed to test their level of proficiency, and we teachers need to take this into consideration when assessing a student's performance. On a more learner-centred note, maybe we shouldn't be afraid to push our students to acquire the more complex structures, even though we know they will easily do without them, because without this extended linguistic knowledge they might not be able to come back to the simple structures and use the language naturally. I might be completely wrong but that's how I feel it being an L2 learner myself.