The teaching of grammar is discussed from an instrumental point of view: what beneficial effects does such teaching have for students' language abilities (especially writing)? Two ways of approaching grammar teaching are confronted with each other: the learning of explicit rules and meta-linguistic knowledge about language on one hand and learning without awareness of linguistic structure (implicit learning) on the other hand. The article shows that implicit learning is more important than is often realised for acquisition and for accurate and fluent mastery of linguistic structures. In addition, research evidence both in mother tongue and second/foreign language contexts shows that explicit learning of structures is not very effective. For the improvement of writing abilities, other forms of teaching are far more effective than explicit grammar teaching. Conceptual processes in writing presumably have a greater impact on text quality than students' explicit knowledge of linguistic structure. Although the explicit learning of linguistic structures is not very effective, there are many other topics for linguistic reflection in the classroom that may have more beneficial effects on students' language use. Some examples of these topics are given, together with theoretical reasons for their instrumental validity in elementary and secondary education. (Contains 1 table and 1 footnote.)