In my 13 years of teaching English to speakers of other languages, Reading Explorer by National Geographic is the best tool I have discovered to build reading skills.
The image to the left is from China's Taobao. In China, Reading Explorer comes as a set of 6 books divided into levels starting at Foundation and going up to Level 5.
In Hong Kong, the set I bought was just 4 levels - Beginner, Elementary, Intermediate and Advanced. The 4 books contained more or less the same material as the 6 books. The books were simply divided differently so the Hong Kong books had more pages in each book. The cost is higher in Hong Kong than in mainland China IF the version you buy in Mainalnd China is printed in China.
If you buy online, you'll want to check to see if you are getting a physical book or online book. Also to see if it is the latest edition. The images shown are for the 2nd edition which is what I bought when I was in China.
In the US, Amazon.com sells the books, but as you might expect, the price is higher in the US than China. While checking for this blog, I noticed the US Amazon site shows a newer edition. They now have the 3rd editon. It does appear the US version now has the same 6 levels as China starting at Foundation and ending at Level 5. The US Foundation, 3rd ed version is shown below the Chinese Taobao advertisement image.
Sample: Below is a scan from the first Reading Explorer Book I bought in Hong Kong from what I guess is the First Edition of the book. It will let you get an idea of how the books may help you.
Each Unit has a Theme. Each unit has a different theme from the other units so you will get exposed to a lot of topics. Here I chose Unit 2 - Favorite foods. Everyone likes food, right?
Note this page asks you questions BEFORE you start reading. This is generally about the broader topic and just to get you thinking about the topic.
Now you get to the first page of the reading. Again, it asks you questions BEFORE you start reading. This is one reading skill. Predicting and thinking what you might read about. They also give you a topic related image.
The first actual reading part of the Unit. The lines are numbers and words are highlighted in red. These are the key vocabulary words they want you to learn. Note the reading section here isn't very long. 1 page.
Next is a section USING the new vocabulary including other forms of the word. Maybe the reading used the noun and now they see if you can understand the adjective or the reading uses one tense and now you need to use a different tense.
You have just finished 1 part of the Unit. Congratulations.
As you can see, it doesn't take much time to do 1 part. 5 pages total with 1 page being reading.
Next comes a second related reading topic.
This section follows the same order as the first section of the Unit.
Now you know why I chose the 2nd unit - one of my favorite foods - chilis / chiles / chilis. As I mentioned at the beginning, this particular book is a little out of date now. It was the first edition and today they are on a 3rd edition. The Ghost chile is no longer considered the hottest in the world.
There are 2 final sections but they are shorter. Just one page with a shorter reading and some questions followed by
a page of questions.
The final section is designed to watch a short video and answer questions. I just discovered I didn't scan those 2 pages but ot resembles the above 2 pages but refers to a video. The video DOES NOT come with the book or at least it didn't come with mine. I suppose they want you to buy it separately. Note the answers to all the exercises are also NOT included with the book. They sell a teacher's book that has the answers but I never bought one.
So that is how Reading Explorer by National Geographic and Cengage Learning is laid out.
Reading is the best way to improve vocabulary and also helps with learning grammar since you see it being used. I had every one of my IELTS students using this material to mprepare them for IELTS - it helps both with the reading sections of IELTS, the listening sections (If you understand the topic you are listening about it improves your recognition of what they are saying) and writing and speaking - again the knowledge of different topics you gain help you talk and write about the topics they give you on the exam.
Maybe this will be useful to some of you.
I have no idea what countries have these books available and which ones don't except I know China and the US has them.