There are a number of factors influencing ESL students' performance in class. If they are Asian students, one of the factors is probably a very high respect and even love for learning. Their cultures have instilled in them a motivation to study and acquire knowledge. At the same time they have been taught to respect the teacher and never to question authority, so to admit they don't understand you would be unacceptable behavior. As for widely disparate abilities in speaking versus reading and writing abilities, that's a very common occurrence since the more academic reading and writing skills are usually acquired somewhat after speaking and listening skills.
Language learning takes a long time, approximately five to seven years.
But my ESL students are high school graduates from public schools. The public schools don't have any exit criteria for ESL skills, which may be only fair since they don't offer much in the way of ESL instruction. Since the summer of 1993, the English as a Second Language instructors at HCC have met extensively in an effort to make major changes in the ESL program here. The proposals have been submitted to the HCC Administration for consideration. For about three years now, the ESL teaching staff have focussed attention on the three levels of classes that, at present, make up the English Language Institute Program.