At the behest of a colleague, I’m taking a time-out from my current series of diatribes against the current state of the American education system and posting this public service announcement.

If you’re just starting test-prep this summer and looking into take a class or working with a tutor affiliated with a company, please tread carefully when dealing with the free practice tests offered by these organizations.

Many of these companies do not use official material produced by either the College Board or the ACT, but rather rely on tests written in-house and used only by the company. This is always the case for national chains such as Kaplan and Princeton Review, and is common practice among other companies as well.

While these tests will usually give you a rough idea of where you stand, and may in some cases provide an accurate picture, they are just as likely to be misleading.

First, no third-party can exactly reproduce the style and nuances of the actual exam; some concepts may be overemphasized, while others are omitted entirely. Questions may be too easy, or too hard, or hard in the wrong way; efforts at capturing “trickiness” often go awry and end up as merely confusing and ambiguous instead.

As a result, students are likely to obtain an incomplete understanding of how their relative strengths and weaknesses affect their performance on the actual exam — both in terms of content and in terms of “softer” factors such as time management. They may also end up unaware that certain concepts are even tested at all.

The second major reason to be careful with these tests is that some companies may artificially deflate scores in order to provoke anxiety and thus induce parents to hand over their hard-earned dollars for classes that may not meet students’ needs, or that even be unnecessary.

If students decide to go elsewhere for tutoring, the result is often a headache for both tutor and student. The tutor does not have a complete and/or accurate picture of where the student is starting from and of what needs to be worked on, effectively requiring both parties to start from scratch.

In order to obtain reliable information, the student must then sit for a second full-length test, this time using official material — and no one really wants to spend an extra 3.5 hours of their summer vacation taking a practice standardized test.

Furthermore, if only a limited number of sessions are planned, time that could have been spent focusing on real problem spots is instead wasted just figuring out what the problems are. (In fact, my colleague urged me to post this warning precisely because she has repeatedly encountered this situation.)

So if you’re considering signing up for some form of paid test prep, please do yourself and your parents’ wallet a favor: block off a few hours, find a quiet spot at home or at a library, sit yourself down with a watch and a College Board- or ACT-produced test, and get to work.

And if you do feel the need to go to a testing center and simulate the full experience, do some research and see whether there’s a place near you that uses official material, or that will let you bring your own test if necessary. It may be a minor hassle in the short term, but at least you’ll start off with a clear idea of what you need to work on what might be involved — information that will help you get off the best possible start.