Hi, Yes it's possible to study and pass any of these tests. The impression I get from most people is that they think they must first know the subject before even considering whether or not to take the tests. In reality this is not the case. Find what you want to learn about and then go from there.

Here's the deal. Most of us on this forum go to one of the big three. They allow GENEROUS credit transfer. Most "state" schools severely restrict the number, type, and quantity, of units they allow to transfer in because of one reason- Money! If you are considering going to Oregon State you need to first talk to an advisor about what will and will not transfer in. Most traditional schools severely restrict or entirely exclude DSST and CLEP tests because (again) that's money lost.
In some cases advisors will only help you after you are an enrolled student. DSST & CLEP's are NOT guarenteed units. Do some serious research (AND GET IN WRITING) permission before taking these tests if you wish to apply them to a traditional school.

Having said that. The Big three are much more liberal in what they will take. I go to Excelsior (excelsior.edu) and they will take just about anything under the sun. If time & flexibility is an issue, it might be worth looking into. Perhaps some of the CO & TESC students can chime in.

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The best things in life aren't things.
~Brandon