Achievement Gap Calculator

An achievement gap is the observed disparity in academic performance between groups of students, often defined by race, ethnicity, income, English learner status, or disability. These gaps are typically measured using standardized test scores, graduation rates, or other academic benchmarks. Identifying and tracking achievement gaps is the first step toward designing interventions to close them.

Cohen's d is a standardized effect size measure that expresses the difference between two group means in terms of standard deviations. It's useful for achievement gap analysis because it allows comparisons across different tests, grade levels, and subjects — unlike raw score differences, which vary by scale. A Cohen's d of 0.2 is considered small, 0.5 medium, and 0.8 or above large.

The pooled standard deviation is a weighted average of the two groups' standard deviations, accounting for their respective sample sizes. It's calculated as the square root of the weighted average of each group's variance: √[((n₁-1)×SD₁² + (n₂-1)×SD₂²) / (n₁+n₂-2)]. This gives a more accurate baseline for the effect size calculation than using either group's SD alone.

The projected years to close the gap is calculated by dividing the current raw score gap by the difference in annual growth rates between the two groups. For example, if Group B grows 1.5 points per year faster than Group A and the current gap is 11 points, the gap would close in approximately 7.3 years — assuming growth rates stay constant. If Group B's growth rate is equal to or slower than Group A's, the gap will not close.

You should enter the average points gained per year on the specific assessment being used. Research-based norms from sources like NWEA MAP Growth or state assessment trend data are good references. Typical annual growth rates range from about 2–6 points per year depending on grade level and subject, with growth generally slowing at higher grade levels.

Yes — simply select the relevant subject from the Subject Area dropdown. The underlying calculation logic (effect size, raw gap, and gap closure projection) is the same for both math and reading. Running the calculator separately for each subject lets you compare where gaps are largest or where interventions may be most needed.

If Group A's annual growth rate is equal to or greater than Group B's, the gap will remain the same or widen over time regardless of current scores. This result signals that the lower-performing group needs a meaningfully accelerated rate of growth — not just matching the higher group's growth — to reduce the disparity.

While the calculator will run with any sample size, results are more statistically reliable with larger samples. Most state accountability systems require a minimum subgroup size of 20–30 students before reporting achievement gap data publicly. Small sample sizes can produce effect sizes that vary widely and may not reflect true group differences.