Pupils learn grammar on the one hand in deducing rules and definitions, on the other hand in doing exercises. The role played by exercises in acquiring grammatical knowledge is being understood unilaterally. A research has been made, which has shown that in doing exercises pupils not only apply a certain rule or definition to a concrete example, but they also carry out abstraction and generalization. If the exercises are unsuitable, these processes of the mind may lead to wrong knowledge, even if the pupils do know the respective rules and definitions. It would be wrong to lay stress on the knowledge of rules and definitions at the expense of learning language phenomena through exercises, i. e. to overestimate the influence of rules and definitions on the acquiring of knowledge, and to underestimate the influence of exercises. It is also wrong to presume that exercises only serve to consolidate the pupils’ knowledge, and that through them pupils only learn how to use their knowledge. By means of exercises their knowledge is being perfected,