Some childhood gaps are welcome news, like that of a gap-tooth smile. Achievement gaps? Not so much.

What is an achievement gap?

An achievement gap is a durable pattern of differences in academic performance between groups of students. Commonly measured achievement gaps include standardized test score patterns by gender, by race/ethnicity, by socioeconomic status, and by degree of English fluency. In addition to test scores, academic achievement gaps can be measured using graduation rates, college-going rates, and course grades.

There are some good reasons to measure achievement gaps using standardized test scores. They are widely used and understood. They can reveal small differences or trends. They are comparatively quick and inexpensive. They also seem to correlate powerfully with variables that are harder to measure. Students with higher standardized test scores are more likely to persist in school, graduate, go to college, and succeed there.

Poverty strongly correlates with test scores. Students who qualify for free or reduced-price lunch services (not really a measure of poverty, but of low income) tend to score lower on tests than those who don't. Race/ethnicity correlates, too: on average, Black and Latino students tend to score lower on standardized tests than white and Asian students do. Achievement gaps are a symptom of a deeper issue — opportunity gaps — where a lack of generational wealth in low-income communities, especially communities of color, results in fewer educational opportunities for students. This term acknowledges systemic disadvantages.

How are achievement gaps measured?

Describing patterns of difference turns out to be more difficult than it might seem, even using test scores. After a student takes a standardized test like the CAASPP, California's state tests, a complex process grades the test using a scaled score. It's more than just counting the number of questions you get right or wrong. Some questions are harder than others, so they are worth or weighted more than easier ones. Some questions are worth nothing because they are experimental.

A test score without context is meaningless, so test designers identify performance tiers, assigning benchmarks that indicate whether students have met expectations. California's system separates scores into four tiers.

Let's suppose that you and your twin sister each take a test, say the grade 5 CAASPP test in mathematics. Your sister scores 2,527 scaled points. You score 2,528—one point higher.

Your parents receive two envelopes in the mail with the score reports. Tearing open the first envelope, with warmth in their heart they learn that your score indicates "Standard Met." They open your sister's envelope, and the warmth fades. Alas, your sister's score falls short. It lands in the "Standard Nearly Met" range.

Of course, the one-point "gap" between these hypothetical scores is insignificant from a statistical perspective. If you both retook the test, your scores would probably be similar but not the same. Like free throws in basketball, there's skill involved, but a bit of randomness, too.

Randomness becomes less important when small samples like this are combined in larger numbers. The close calls on either side of the line tend to cancel one another out. Unfortunately, the statistics show that there are some big gaps.

How big are the gaps?

They're big. Here's a comparison of CAASPP scores by subgroup for English Language Arts:

The gaps are big for math, too:

Are achievement gaps shrinking?

Achievement gaps have proved to be deeply durable. Change does happen, but it tends to take generations, not mere years or decades. For example, today girls tend to score higher than boys, a reversal. But gaps among racial/ethnic groups remain large. From 2014-2024, the pattern remained basically flat:

It could be argued that the years presented in the chart above were unusual. California’s grade-level standards and state tests were shifting to match the Common Core. There was a pandemic. Families got out of the habit of bringing their kids to school every day, no matter what.

For the decade prior to 2014, California had used a different set of annual assessments, the California Standards Test (CST). During that period, tests showed a steady pattern of rising scores across all groups of students in both English and math.

Source: CA Department of Education. Click for additional detail

Taking the long view, educational optimists see the decade 2014-24 as a series of unfortunate events that interrupted a positive long-term trend toward proficiency for all students.

What is proficiency?

Academic proficiency means mastery of the subject-matter knowledge and skills specified for a student's grade level. As a practical matter, proficiency is defined by test scores. When looking at any chart that compares "proficiency" rates, squint a little. Remember, individual scores are pesky, detailed things. A little bump can push a score over the cutoff line between one achievement category and the next. Cutoff points are defined by a rule, not by a force of nature. They are supposed to represent a standard of achievement, not a relative position within a curve.

Education statistics are loaded with metrics derived from cut-off scores. By the nature of statistics, if a cut-off point stays put while a curve moves, metrics that describe how much of the curve falls above or below the cut-off point will highlight the significance of some changes while understating others. If the cut point is anywhere close to the steep part of the curve, a little bit of change can cast an exaggerated shadow.

Bell curves have two tails, and some critics argue that reducing gaps by boosting the learning of kids at the bottom of the learning curve isn't enough. They argue that long-term American competitiveness requires that a school's mission should include a focus on gifted kids at the top of the curve, too.

The success of California's schools, districts, and public education system as a whole is often judged by how effectively they address these predictable gaps in achievement. The next lesson discusses the ways these systems' successes are measured.

Updated December 2024