In this study, the resemblance of the language learning course books used in Turkey to authentic language spoken by native speakers is explored by using a corpus-based approach. For this, the 10-million-word spoken part of the British National Corpus was selected as reference corpus. After that, all language learning course books used in high schools in Turkey were scanned and transferred to SketchEngine, an online corpus query tool. Lastly, certain grammar points were extracted first from British National Corpus and then from course books; similarities and differences were compared. At the end of the study, it was found that the language learning course books have little similarity to authentic language in terms of certain grammatical items and frequency of their collocations. In this way, the points to be revised and changed were explored. In addition, this study emphasized the role of corpus approach as a material development and analysis tool; and tested the functionality of course books for writers and for Ministry of National Education.