TOEFL is a vocabulary test. I hear this all the time. And it is wrong. The TOEFL iBT is not a vocabulary test. It is an English-language proficiency test whose main testing tool is the argument (the essay). If you do not understand basic argument development (read: basic western style rhetoric), you will not score above 90/120. I know. I see this all the time.
Yes, a large vocabulary is essential when taking the TOEFL iBT, but it is only one part of a proficient argument. Think of it this way: Vocabulary is like the cheese on a cheeseburger, the cheeseburger being your argument. If the cheese is cheap processed cheese, you know, the stuff that tastes like plastic, the cheeseburger will taste terrible. Ah, but if the cheese is aged Wisconsin organic blue cheese - now that's an argument for a great cheeseburger! Note in this analogy how the cheese supports the meat, just like vocab supports an argument (the main meal).
Spread the word. TOEFL is not a vocabulary test. The TOEFL iBT is an English-language proficiency test whose main testing tool is the argument. That is what my TOEFL texts teach. That is why my TOEFL texts are different from all the rest.