Placing students into remediation involves an important decision, especially for the student. You'd think by now we would have figured out a valid measure of readiness to succeed at the collegiate level.
Unfortunately we aren't there yet, according to an article by Ashley A. Smith, in Inside Higher Ed. If you have anguished over this problem, you have plenty of company. The writer takes a look at practices at community colleges around the country.
The most popular strategies for placement look familiar: standardized tests and high school GPA. Community college teachers know from experience that both techniques are flawed. Standardized exams are notoriously unreliable, especially for students who have been out of school for a while. But tests are better than nothing. As for high school GPA, we all witness students with high ranking who are unable to tackle introductory mathematics such as algebra or read at the ninth grade level.
Most authorities recommend a blended metric as the best approach to placement, assuming certain numbers are available in a student's previous record, which is a problem. But by combining variables perhaps we can use the strength of each factor.
There is no magic algorithm. That's one takeaway from the article.
Now here's the weird part. When you visit with instructors they will tell you that they can, in a few minutes, determine a student's readiness. In math, a handful of problems on paper are very telling. With English, a brief essay is all you need. There are exceptions, of course, and subjectivity is rightly open to criticism. But it's unfortunate that such a rudimentary technique isn't scalable upon enrollment for everyone.
Mistaken diagnoses are inevitable with any strategy, but simplicity should be a fundamental goal.