Grammar is boring, but how can native speakers write academically, without mistakes, without knowing the grammar rules they learnt in high school? Most natives learn grammar when they are in school, and forget all of it.
One should distinguish between implicit learning and explicit learning. According to Wikipedia, there is no agreed-upon definition of implicit learning, so we assume the following rough definitions of implicit and explicit training:
- explicit training is "training that provides learners with information about (...) grammar rules or directs them so search for rules", and
- implicit training is "training that engages (...) learners with the target language but does not provide any explicit information or direction to search for rules".
(The above definitions are borrowed from "Explicit and Implicit Second Language Training Differentially Affect the Achievement of Native-like Brain Activation Patterns" by Morgan-Short et all, 2011; the authors used "Effectiveness of L2 Instruction: A Research Synthesis and Quantitative Meta‐analysis" by Norris and Ortega, 2000, as a source.)
Children start learning their native language long before they begin attending school and they acquire a lot of grammar without being told what the grammar rules are; this is an example of implicit learning. By the time they start attending school at the age of 5 or 6, they already know all the basic grammar rules, even though they can't formulate them explicitly. (Their parents typically can't formulate those rules either, unless they are linguists or language teachers.) This is an example of implicit training.
School children don't start learning grammar from scratch; the language teaching at school builds upon a basis that the children already acquired outside school. In order to refine the grammar knowledge that the children already have, teachers provide a lot of explicit training. For example, native speakers of Dutch already know how to say, "ik rijd" (I drive/ride), "jij rijdt" (you drive/ride) before they go to school. In both cases, the verb (rijd/rijdt) is pronounced exactly the same, but the spelling is different; teachers teach children the rules for the correct spelling of verb forms, e.g. using the mnemonic 't kofschip.
In some languages, much of the explicit grammar training is tied to
- more advanced vocabulary that children need to acquire (e.g. in German: prepositions that should be used with the genitive in formal language, even though they are typically used with the dative in informal language; most German prepositions with the genitive express relationships that children learn later or that they express in less accurate ways);
- grammar that is required for good writing, e.g. complex syntax and "text syntax".
(Above, I wrote, "in some languages, because the amount of explicit grammar learning differs from language to language. For example, at least one of my Chinese tandem partners told me they were never taught grammar in school.)
Even though people forget the explicit rules, this does not mean that this knowledge gets lost, for two reasons:
- using the rules repeatedly leads to automation: after a while, you know that a specific expression or structure is correct, because you have used it so often, so forgetting the explicit rule does not a loss of grammar knowledge;
- implicit learning still continues: the grammatical structures you learn explicitly are also found in spoken and written texts, and since humans are excellent imitators, they continue to learn new grammatical structures outside the classroom.
In short, explicit training of grammar rules is like learning to ride a bike with training wheels. After a while, you have learnt to keep your balance and you can continue without the training wheels.