In recent years, a reactive focus on form in ESL pedagogy has maintained a steady level of popularity in the teaching community.

Second language acquisition theory came to prominence in the 1980s and has been the dominant ideology in ESL instruction for the last two decades. Form is not a privileged component in second language acquisition theory; the study of language form is not considered applicable to the learning of language, but rather is seen to be merely a study of the appreciation of language or linguistics.
Research in the field of Rhetoric and Composition of the last several decades has also failed to uncover meaningful connections between the study of language form and improved reading and writing abilities in students. However, given enough time, what is old always finds a way to become new again, especially in education. Instructors are again thinking of ways to treat form in the ESL classroom in a more substantial and tangible manner.
The premise of reactive focus of form in ESL basically equates to error correction. A student completes a writing exercise and turns it in for evaluation. The instructor addresses the mistakes made in the writing by actively correcting them for the student. The error that the student makes is the starting point for the discussion about that particular linguistic situation. This focus is also referred to as the negative feedback model.
This reactive focus reflects the traditional stereotype of an English teacher returning a paper to a student that is filled with red ink. Some in the field today negatively refer to these red ink filled papers as "bleeding." The instinct for many instructors has long been to show students what they are doing wrong so that they can understand where they made mistakes and learn how to not make the same mistakes in the future. Letting an obvious error go by without calling attention to it was akin to telling the student that the error never happened and creating a false sense of capability.
The problems with this type of focus on form have been numerous. First of all, most students don't know the rules of grammar sufficiently to make any sense of the error corrections that teachers make on their papers. If they knew the rules, they likely would not have made the mistakes in the first place. Given the many context dependent variables, exceptions to the rules, and general inconsistencies that exist in the English language, scratching out a word on a student's paper and writing something like "needs to be in irregular form" above it will more often than not mean nothing to a student.
In addition, teachers that comment on every mistake made in an essay can very easily overwhelm a student. Research suggests that reactive focus on form works best if an instructor picks one or two issues that the student makes in a paper and draws attention to those, leaving all other mistakes alone. If the student begins to grasp the errors that you are focusing on, the instructor can begin to call attention to different types of errors.
Finally, there is a psychologically negative effect of returning a paper that is "bleeding" red ink to a student. Most students who struggle with writing are very aware that they struggle. For the student who works diligently on a paper, too many error corrections send a discouraging message.
In recent years, the trend in ESL pedagogy is moving away from this type of focus to what is know as the preemptive focus on form method. In this method, instructors and students make a conscious decision to make a particular aspect of form a part of the discourse before undertaking a writing assignment. Instead of letting errors dictate the discourse, this method chooses to anticipate problems and focus on the students' abilities to "uptake" a particular form. Uptake refers to the act of taking a new form and correctly incorporating it into a student's speaking and writing.
Much of the research on reactive focus on form in ESL is published in professional journals like JSTOR. Access to the articles typically requires either a subscription or an affiliation with a university. Sometimes, university libraries will give non-students access to their resources if they are conducting research, although arrangements typically need to be made in advance.