There are some educational issues that have become so covered with layers and layers of detail and nuance and policy and jargon and baloney and nature's own fertilizer that it can become difficult to see the relatively simple problem that lies beneath the giant mounds of stuff.
Closing the achievement gap is one such issue. It's the subject of considerable discussion and policy wrangling, and is the raison d'etre given for a variety of programs. But let's talk about what's really going on here. There are two ways to discuss closing the achievement gap, and only one of them is remotely useful.
Let's say that all students have to run a 5K race. The distance between the lead runners and the last-place runners is our Racing Gap.
If we're going to close the gap in one race, here's what we have to do. Chris is up front, leading the pack. Pat is far behind. Pat is behind because Pat runs slower. If we get Pat to run as fast as Chris, that just keeps the gap static. In order to close the gap, Pat-- who is demonstrably our slowest runner-- must run faster than Chris-- who is demonstrably our fastest runner.
This is nuts.
We can close this achievement gap one of two ways-- we can either strap Pat to a rocket or car or other faster-than-human conveyance, or we can weigh Chris down, Harrison Bergeron-style, so that Chris runs slower. Neither option is okay.
Trying to get everyone to run faster will help them beat their old times, but it will not close the gap. In fact, it will probably make it worse, just as giving all workers a 10% raise would make the pay gap worse.
Now, the achievement gap is not a completely useless construct if I work on a larger scale. If I look at the gaps over long stretches of time, I might see some trends that help me diagnose a problem. If Chris's parents beat Pat's parents by twice (or half) as much as Chris beats Pat, that might suggest that something has changed (though good luck narrowing down what, exactly).
But that's only a sort-of-useful diagnostic tool. Whether gap widens or narrows is symptomatic of something, but it's far more useful to try to address underlying problems than to simply try to make the symptom go away. The focus on closing the achievement gap is the same sort of myopic focus on massaging the numbers instead of addressing reality that infects so much of reformsterdom and leads us to ridiculous solutions like trying to figure out ways to make the slowest runners run faster than everyone else.