Something like this just happened in the San Francisco school district. As of last month they decided to undo a key piece of an Ivy League authored school assignment algorithm and there's talk of scrapping the whole thing.[1]

If you know a parent with small children in SF you've probably have heard some consternation about the school lottery. Although the majority of families get their first choice, there are copious horror stories. Top economists were brought in around 2010 to design a new school assignment system.[2] They designed an algorithm. It tried to solve for a few goals: diversity, proximity and choice. They tried to make it "strategically simple" to avoid gaming the system.

The algorithm works like this: You rank the schools you want. Assignments are handed out according to a series of preferences called tiebreakers: First to siblings, then residents of low test score areas (to promote diversity), then residents of the neighborhood, then by lottery draw. If you didn't get anything on your list it'd assign you to the nearest school with space.

Then it did a neat thing: If it saw a mutually advantageous trade between families, it'd do it. If Family A got B's top choice and B got A's top choice they'd both get upgraded. It's called the Transfer Mechanism, commonly known as "swapping". This was meant to cut out complex strategies to get the school you want so you could just honestly list the schools you wanted in order.

Welp... After many years of horror stories of families getting assigned clear across town, the verdict finally arrived that the system utterly failed to improve diversity too. Here's what's going wrong:

1. That low test score area preference (called CTIP) is disproportionately used by the few white and asian families in those neighborhoods to get out of their local school. It's a golden ticket to any school in the city. Perversely, what was meant to help diversify actually increased segregation while rewarding the most privileged families.

2. The neighborhood preference (called Attendance Area) is woefully inadequate to ensure assignment to a nearby school. Many schools don't have enough capacity for their area, and if you don't get into your neighborhood school the other nearby schools might also be filled up by their own locals. That means you could be assigned clear across town to the nearest school with capacity -- which means not a very popular school either. No consideration is given to "bumping" a set of people over one neighborhood, for example, or otherwise more gently distributing the pain. (EDIT: I just noticed the original proposal had an "Overfill" preference to address this very issue.[2] Didn't get implemented.)

3. Far from simplifying strategy, the Transfer Mechanism actually opens up a whole new kind of strategy. Clever families list schools with "swap value" in the hopes that they'll transfer their way into an otherwise inaccessible school. This is exacerbated by the existence of speciality schools that don't have an Attendance Area preference, i.e. language immersions and K-8 programs, creating a kind of niche swapping opportunity with AA-bearing families. This results in excessive "false" applications to these speciality schools, bumping more "true" applicants to their oversubscribed local school, bumping other locals, replacing them with swapped-in clever families, and creating a sense of injustice. Worst of all, this strategy is, you guessed it, disproportionately utilized by privileged families.

So last month SFUSD just decided to suspend the Transfer Mechanism.[4] This is big news and I'm not sure most families realize it yet. And there is a proposal in the works to rethink the whole system, taking inspiration from Berkeley.[1]

[1] http://www.sfexaminer.com/school-board-member-proposes-scrap...

[2] http://web.stanford.edu/~niederle/SFUSDBoardPresentationFeb....

[3] http://www.sfusd.edu/en/assets/sfusd-staff/enroll/files/2019...