For starters, when the elementary and middle-school students come back next fall, there won't be any grade levels – or traditional grades, for that matter. And those are only the most visible changes in a district that, striving to reverse dismal test scores and a soaring dropout rate, is opting for a wholesale reinvention of itself, rather than the incremental reforms usually favored by administrators.
Scheduling is a big one. It's also unclear what will happen if large numbers of kids arrive in high school still unable to demonstrate proficiency in certain subjects, like math, and a bottleneck gets created. Since no student can move forward without a "B" equivalent, it's also essentially impossible for students to have lower than a 3.0 GPA, which could be a challenge to explain to colleges.