Well... it is 2019 though... I hope it is not bothering to answer this 2015 question. It varies from person to person. In middle school and high school (maybe even elementary school), students will come across come Kanbun(漢文) and we call it Classical (or Literary) Chinese (文言文). It is believed that it is spoken Chinese in 秦朝 or before it. Although it is written in a compact way, it is believed to be spoken language at that time, when people wrote on bamboo （竹簡）and the space is limited so people had to shorten the sentence. However, the language develops. The spoken Chinese started to deviate from what is spoken before. At least in 漢朝, the spoken language became very different. But at that time, 論語 became a classical text and every scholar studied it. So those who are educated is able to written in the way that 論語 is written. Since then it becomes a tradition that the written and spoken Chinese are different. During hundreds of years, the spoken Chinese develops and varies, but the written Chinese remains and spreads. Even today, the high school students (who spend a lot of time on it because we test it in Gaokao) can understand the basic meaning of a piece of classical Chinese. For high school Chinese teachers and those who continue to study them in university, I believe they can understand most of classical Chinese easily. Moreover, it depends on which sentence of classical Chinese too. Some are really straightforward, while some are confusing. For example, we studied 《師說》(see https://zh.wikisource.org/wiki/%E5%B8%AB%E8%AA%AA) whose author is 韓愈 (768-824). The first sentence is "古之學者必有師", I believe any Chinese people today can understand it. At least before 1949, it is still prevalent to differentiate written Chinese from spoken Chinese. But today we write almost in the same way as we speak. So in all, most Chinese can read some and for those who are educated, they can read more. For those who spend time on it such as high school teachers, they are fluent.