Hiya Courtney
As someone who went through the process many moons ago, I'd have to say explore both routes (booking a pro and doing TF). A simple pro-shoot will give you the essentials needed for a basic starting-out portfolio (nice clear quality headshots, three-quarter shots, full-length shots, etc.), but lets face it, a good photographer can make anyone look like a model.
The TF shoots will give you the depth in your portfolio which you'll need to be able to justify charging. And it will show that you can get good results from a wide variety of shoots, not just one shoot where a professional tells you what to do the whole time. Having the ability to pose yourself is key in getting paid work.
And don't forget references - TF shoots help you build a list of references which is just as important, to show you're able to turn up to a shoot (something that not everyone has the ability to do, strangely enough). And word of mouth is important too - models and photographers talk, so building up a good professional reputation will help you go far.
The idea that you can start charging after one shoot with a pro photographer, without putting in the time to learn and gain experience, is why many photographers get frustrated. It's also why new models get frustrated and quit because they don't understand why they're not getting work. And everyone ends up bitching about the whole thing in the forums.
Seeing as you are rather young, you've got all the time in the world, and a lot of paid work will be for shoots that you're unable to apply for (as in the UK you're classed as a minor until you're 18 ). But that just means that by the time you're 18 and able to whatever shoots you like, you'll have a massive portfolio and list of references that the other 18-year-olds just starting out won't have, and it will make you very marketable.
Anyway, just my thoughts, but I thought a model's opinion might be helpful in this case.
