Research has shown us that it is not necessarily so. Student disengagement is, indeed, believed to begin at an early age (but not kindergarten, more like 3rd grade), and it reaches its pick in high school. However, a high-performing elementary school student may end up being a low-performing high schooler, and vice versa. If middle and high schools are poorly organized, even the best lower-grade program will not improve graduation rates.
Traditionally, public moneys have been allocated to the lower grades, and look where we stand as far as high school graduation goes. I think that this is the main reason to my objection - it is highly popular to focus on the lower grades, and the system ends up with a neglected middle/high school system and rediculous graduation exams.