Key to ranking schools in DC school lottery might surprise you

Many parents wonder how they should rank their schools in the My School DC (MSDC) Lottery to maximize their chances of getting a good match. We dug into the algorithm to understand the absolute best way to rank your choices. What we found might surprise many people. 

How You Should Rank Your Preferences

The key to having the best lottery outcome possible for your child is to completely ignore school popularity when ranking them. You should only rank schools based on how much you like them. Putting a very popular school at the top of your list will NOT hurt your chances of getting into your lower choices. Conversely, ranking a slightly less personally-favored and generally less popular school higher will not increase your likelihood of getting accepted into that school either; it might, however, mean you do not even get on the waitlist of a more desired school because you ranked it lower. The algorithm cannot be “gamed” in this manner. The only way to improve your likelihood of getting into a school is by being randomly assigned a higher number in the lottery which, of course, is out of your control.

Here is a quick example: Let’s say you have only two schools you are interested in. School A is your #1 choice, but you have heard it is extremely hard to get into. School B is your #2 choice and is a lot easier to get into. Do not pay any attention to how hard School A is to get into. You should rank School A first in your MSDC list – you like it more and it is your #1 choice. You will not improve your likelihood of getting into School B by ranking it first and will not be on the waitlist for School A if you are matched with School B.

One caveat: For parents interested in more than 12 schools, you might want to consider the perceived difficulty of getting into those schools and include one or more schools with a higher match likelihood. When deciding which 12 schools (this is the maximum number you can include on your list), you might consider taking popularity into account for your final list of 12, but when ranking them you should not. In recent history, 78% of all applicants selecting the maximum of 12 schools have been matched with one of them via the lottery algorithm and 84% of all applicants the last 3 years were either matched with a school or received a waitlist offer.

Why the Lottery Algorithm Works This Way

Some people find this to be counter-intuitive to their perceptions of lottery matching systems and based on what they have heard from other parents and lottery advisers. That is because the computer program MSDC utilizes is designed to maximize student-to-school matches while obeying preferences and ranks without inherently advantaging any applicant. Other lottery matching systems attempt to maximize the total number of #1-ranked school matches. In those lotteries, not getting into your #1-ranked school might hurt your chances of getting into your lower choices.

MSDC uses what’s called a deferred acceptance matching algorithm. The word "deferred" here is critical. What that means is during the first pass of the algorithm the computer figures out if you are unofficially “accepted” to all your choices at once using your random lottery number and any preferences (sibling, in-boundary, etc.) you have to the school. Then it matches you to the highest ranked school you were “accepted.” If you did not match with your first choice on the first pass, then it keeps including you on each successive pass until it gets you (and every person in the lottery) their highest possible match. Once you are matched, the schools you rank below where you are matched are not processed.

Let’s look at a new example with more schools. Pretend your student’s random lottery number was 14. Here is an example output of one pass of the algorithm, illustrating the key aspects.

Version 1: You rank schools in terms of how much you truly like each school

You can see that it “accepts” your student into any school where the lottery number needed is greater than your random lottery number (14). However, it only matches you with your favorite accepted school. Ranking School A and School B at the top did not hurt your chance of getting into School C.

Also consider that you will only be waitlisted at schools you ranked ABOVE where you are matched. You will be dropped from consideration at all the schools ranked below where you are matched.

Now let’s look at a version where we take popularity into account. Let’s put School E and School G at the top since it is easier to get into them.

Version 2: You take popularity into account

Notice that your student was “accepted” into all the same schools, but they matched at School E because that was your first choice. Only matches count. The system thinks you got your first choice, so it won’t even process the rest of your application and put you on the waitlist for the other schools.

To summarize, you should rank your schools based on the order you like them only. DO NOT rank less popular schools higher just because you think it will increase your chances of getting in. It will not.

So, wait! I heard someone say that families who rank a particular school lower than #1 don’t get in. Is that not accurate?

It’s misleading. If you like the school the best, then you should rank it #1. Changing the order of your schools will not inherently improve the odds of a seat being available when it’s your child's turn in the lottery. The only way to improve your likelihood of getting into a school is by being randomly assigned a higher number in the lottery which is out of your control. What the person said may confuse what happens in the matching algorithm and is a misnomer likely referencing other lottery matching systems, not DC’s. The lottery algorithm will give your student the highest possible match based on their random lottery number.

Still want to dig-in further yourself? Here are some important links to help your research quest.

For a detailed explanation from My School DC itself, check out their video. At 8:33, the video explains how to rank schools. The video also gives you information on other aspects of how the algorithm works.

For our eduDataRazzi wonk friends, read up on the history of the algorithm methodology courtesy of Wikipedia and in this paper by Alvin Roth. Another good article on lottery algorithms is this one from the Center for American Progress (thanks to @betsyjwolf for the reference!) Note that in the literature, the algorithm is called a deferred acceptance algorithm. We changed the word acceptance to "matching" for clarity and alignment with the My School DC terminology of matching students to schools.

For those parents applying to schools in the coming month, we encourage you to tour all schools on your wishlist, including your neighborhood DCPS school, and we wish you the best.