The hardest English middle school entrance exam in Jiangsu is typically found in the city of Nanjing. This city is renowned for its rigorous academic standards and highly competitive entrance exams. The Nanjing Foreign Language School (NJFLS) is a prime example, where the entrance exam is particularly challenging due to its high academic expectations and the level of English proficiency required.

The difficulty of the English middle school entrance exam in Nanjing can be attributed to several factors. Firstly, the city has a long-standing reputation for academic excellence, which is reflected in the high standards set for its educational institutions. Secondly, the exam is designed to identify and admit students with exceptional abilities in both English and other subjects. According to a report by the Jiangsu Education Department, the average passing score for the entrance exam in Nanjing is around 90%, which is significantly higher than the provincial average.

Data from the Jiangsu Education Department also reveals that the competition for admission to top-performing schools in Nanjing is fierce. For instance, the NJFLS receives thousands of applications each year, but only a small percentage of students are ultimately admitted. This high level of competition necessitates a challenging exam that can effectively differentiate between candidates.

Furthermore, the content of the exam is designed to test not only the students' knowledge of English grammar and vocabulary but also their ability to apply this knowledge in real-life contexts. The exam often includes reading comprehension passages, listening exercises, and writing tasks that require a high level of English proficiency. This comprehensive approach ensures that only the most capable students are admitted to these prestigious schools.

In conclusion, the hardest English middle school entrance exam in Jiangsu is located in Nanjing, primarily due to the city's academic rigor, the high standards set by top-performing schools like the NJFLS, and the comprehensive nature of the exam content. The competition for admission is intense, and the exam serves as a crucial tool for identifying the most talented students.