5 years ago TOEFL was substantially different. Recently TOEFL CBT was transfformed into TOEFL iBT which contains one more session - speaking, which is the worst part of the new test and requires some practice.
Sure thing, you cannot learn English in 3 months - there is no preparation program capable of upgrading your score from 0 to 115 in couple of weeks. What prep materials can do is introducing the applicant in to the exam. By using prep books test taker becomes familiar with format of test questions and, especially, essays. Essays for TOEFL iBT are specific and their knowing could add couple of points to ones score - just what one need in order to successfully apply to the school that requires 104 points unstead of 100 like all other schools.
My GMAT experience
My retake experience - GMAT dropped from 720 to 690 - advice for retakers
My TOEFL experience - 108