On many of the other pages of advice on this site I have emphasized how important reading is as far as learning English is concerned. However, there is a further, very important reason why ESL students should try to develop their reading skills: Educational researchers have found that there is a strong correlation between reading and academic success.* In other words, a student who is a good reader is more likely to do well in school and pass exams than a student who is a weak reader.
Good readers can understand the individual sentences and the organizational structure of a piece of writing. They can comprehend ideas, follow arguments, and detect implications. They know most of the words in the text already, but they can also determine the meaning of many of the unfamiliar words from the context - failing this, they can use their dictionary effectively to do so. In summary, good readers can extract from the writing what is important for the particular task they are employed in. And they can do it quickly!
Educational researchers have also found a strong correlation between reading and vocabulary knowledge. In other words, students who have a large vocabulary are usually good readers. This is not very surprising, since the best way to acquire a large vocabulary is to read extensively, and if you read extensively you are likely to be or become a good reader!
So if you want your child to be successful at school encourage him or her to read. Reading non-fiction in English is probably the most important, but English fiction and any reading in the mother tongue - if done extensively - will help your child develop the reading competence that is essential for academic achievement.
The graphic below illustrates the interdependence of vocabulary, reading ability and academic success.
* "Research findings in applied linguistics and reading research consistently show a strong correlation between reading proficiency and academic success at all ages, from the primary school right through to university level: students who read a lot and who understand what they read usually attain good grades." Pretorius, E. [ Source ]