To start, there's the fact that they didn't really make sure it worked first. The committee's report basically turned education into an assembly line. Unless you're an Einstein-level prodigy and get to skip a grade or do really, really badly and get held back, your progress through the school system is more or less decided on the time spent sitting at your desk -- one year equals one "grade." It'd be like an RPG in which leveling up didn't depend on how many orcs you grinded, but simply the number of hours you sat at the computer.
"I'm gonna grind through Junior Prom, then I'm never buying anything off Greenlight again."
Indeed, the Committee's standardization model (which was later refined by the Carnegie Unit) wasn't intended to maximize the quality of schooling so much as its efficiency -- they wanted to "batch process" kids for higher education. After a set period of time, you either memorize enough facts to go on to college or university, or you don't (in which case, ha ha, fuck you). And this 120-year-old system relies on the ability of every kid going through puberty to fully understand the weight of their own mortality and forward-plan the next 50 years of their life in an age in which free Internet porn exists.
And how do we record how well our kids retain this rote knowledge? Standardized testing, of course! And that brings us to ...