Why we publish two series of Chinese textbooks

The short answer is that, due to unique characteristics of Chinese language and its huge differences from most of other modern languages, we believe that the best way to approach the task of learning Chinese is through a clear separation between learning to interact orally and learning to read and write.
The following is a more elaborate answer, along with some must known definitions.
What is Mandarin?
Among a number of dialects which are in active use today, such as Cantonese, Mandarin is the most widely spoken one in the Greater China Region, which includes mainland China, Hong Kong, Macau and Taiwan.
Mandarin Chinese is the modern standard Chinese, China’s official language. It is also referred to as “putonghua” (普通话, the common language), or “hanyu” (汉语, the language of the Han people), or “zhongwen” (中文, the language of China). In Taiwan, it is often called “huayu” (华语, the language of people of Chinese ethnicity), or “guoyu” (国语, the language of the country).
Simplified Chinese
There are two overlapping Chinese writing systems, simplified and traditional Chinese. The simplified Chinese is used in mainland China and Singapore, while the traditional Chinese in Hong Kong, Macau and Taiwan. In Chinese media of other countries, such as in the US or Australia, it is common to see that both versions are used, which is a reflection of the historical roots of local communities.
Both simplified and traditional Chinese are recognised worldwide. It is certainly an advantage to have some knowledge of both systems. However, from teaching and learning point of view, to learn both systems at the same time is too difficult. In Mandarin Express series and Chinese Reading and Writing series, the priority is given to simplified Chinese.
Read more about the simplification process of traditional Chinese characters.
Pinyin
There have been many systems using Roman alphabet to reproduce the sounds of Chinese characters throughout history. And in Taiwan, there is a different system in use, called Zhuyin, which is a list of character-like symbols.
Today, the Hanyu Pinyin system, or pinyin, is the most recognised worldwide, and is also an efficient method of text input. This system can help students of many different language backgrounds. Therefore, pinyin is included in Mandarin Express Intro and Basic Levels.
However, it is important to understand that pinyin is not a valid alternative to the writing system, neither does it lead to natural speech. Read "Why learning Mandarin using (only) Pinyin will create more hurdles" and "The gulf between pinyin and Mandarin Chinese pronunciation" for detailed explanations.
The necessary separation of learning to interact orally from learning to read and write
For beginner students, Chinese literacy development is a time-consuming and challenging task. Learning oral interaction and its written form at the same time is really difficult and can be extremely overwhelming. With the even smallest amount of verbal exchanges, students must tackle the following tasks at the same time:
- to recognise the written form of Chinese characters;
- to associate the pronunciation with each character;
- to be able to write characters;
- to learn the meanings of each character;
- to learn the sentence structure;
- to practice speaking and to form muscle memories of characters, words, and sentences;
- to recognise characters, words and sentences when hearing them.
Students’ time and energy will be spread out too thin to successfully achieve all of these tasks, especially for those who have other commitments in their lives.
Therefore, in order for students to have the best learning result and also to have great learning experiences, it is necessary to disperse these tasks into smaller ones over a period of time. The most efficient way is a separation of learning oral interaction from its written form. It will allow students to develop some speaking capacities quickly, while slowly building up their knowledge of the Chinese writing system.
When students have developed substantial skills in Chinese reading and writing, it’ll be natural for them to combine learning oral communications with its written form.
Two series of Chinese textbooks
Mandarin Express series and Chinese Reading and Writing series do not separate verbal interaction from its written form mechanically, i.e. It is not that one series teaches in pinyin, while the other teaches the same script in characters. The relation between the two series is rather like a simulation of Chinese children learning Chinese. After developing some conversational abilities, students start learning how to read and write.
At Mandarin Express Intro and Basic Levels, when students are developing conversational abilities, the learning medium is pinyin.
At Chinese Reading and Writing 1-6, when students are developing their reading and writing skills, the learning medium is Chinese characters. Chinese Reading and Writing series focuses on 320 Chinese characters, which is a small number comparing to 3000 - 3500 characters normally required to achieve Chinese literacy.
The selection of these 320 characters is based on a Chinese character frequency list, and also on Mandarin Express series. Thus, there is a connection between the two series, creating a re-enforcing learning environment.
After students have a good grasp of Chinese reading and writing and the ability to carry on nice social conversations, they can continue their Chinese study in the subsequent Mandarin Express Pre-Intermediate Level, which combines the learning oral communication with its written form.