It is very important to have a good knowledge of grammar if you are to succeed in any of the international exams. Most of the exams have a section where they test your grammar. You need to write tenses correctly and put words in the correct order in a sentence. In this section you can study grammar and do practice tests by CEF level and by topic.
A1 grammar topics
A2 grammar topics
B1 grammar topics
B2 grammar topics
You can also see which grammar topics are associated with CEF levels.