The What Works Clearinghouse (WWC) is a free, publicly available resource run by the U.S. Department of Education that reviews education research and tells educators, administrators, and parents which programs and practices actually improve student outcomes. Established in 2002 by the Institute of Education Sciences (IES), the WWC applies rigorous standards to published studies and rates whether the evidence behind a given intervention is strong, moderate, or insufficient. Think of it as a consumer-reports-style guide for education: instead of testing appliances, it evaluates tutoring programs, curricula, teaching strategies, and school-level interventions.
What the WWC Actually Does
The clearinghouse doesn’t conduct its own experiments. Instead, it systematically reviews existing research, primarily randomized controlled trials and strong quasi-experimental studies, and judges whether the study design and execution are reliable enough to trust the findings. Each reviewed study receives one of three designations: meets standards without reservations, meets standards with reservations, or does not meet standards.
A study that “meets standards without reservations” is typically a well-designed randomized controlled trial where participants were properly assigned to groups and the dropout rate didn’t undermine the results. “Meets standards with reservations” means the study has some design limitations, perhaps it used a comparison group rather than random assignment, or had higher-than-ideal attrition, but still provides useful evidence. Studies that don’t meet either threshold are excluded from the WWC’s findings.
The WWC then packages its conclusions into several formats that educators can use directly: intervention reports, practice guides, and reviews of individual studies. All of these are available at no cost on the WWC website.
How Evidence Tiers Work Under ESSA
The Every Student Succeeds Act (ESSA) requires schools and districts to use “evidence-based” interventions when spending certain federal funds. The law defines four tiers of evidence, and the WWC’s review standards map directly onto the top two tiers, making it the go-to resource for schools trying to meet ESSA requirements.
Tier 1 (Strong Evidence): An intervention qualifies here when at least one study meets WWC standards without reservations, shows a statistically significant positive effect, includes at least 350 students, and spans at least two school sites. For a school or district to claim Tier 1 status for a program, the study’s student population and setting must overlap with the school’s own population and setting. A program proven effective with suburban high schoolers doesn’t automatically count as Tier 1 evidence for a rural elementary school.
Tier 2 (Moderate Evidence): The bar is slightly lower. A study can meet WWC standards with or without reservations, but must still show a statistically significant positive effect across at least 350 students and two sites. The contextual requirement is also looser: the study’s population or setting needs to overlap with the school’s, rather than both.
Tiers 3 and 4 under ESSA cover correlational studies and programs with a strong rationale but limited research. Those tiers don’t rely on WWC review standards, but the clearinghouse still helps educators identify where a program falls on the evidence spectrum.
Topics and Grade Levels Covered
The WWC covers a broad range of education topics. Its searchable database lets you filter by subject area, including literacy, STEM, social-emotional learning and behavior, college readiness and completion, career and technical education, high school completion, school choice, and out-of-school learning. It also addresses specific student populations, with dedicated categories for English learners and children and youth with disabilities.
You can filter results by grade band as well: preschool, elementary (K through 5), middle school (6 through 8), high school (9 through 12), and postsecondary. This makes it straightforward for a third-grade reading specialist or a high school principal to find programs reviewed for their context without wading through irrelevant research.
How Educators Use the WWC
The most practical entry point is the search tool on the WWC website (ies.ed.gov/ncee/wwc). You select your topic, grade level, and the type of resource you want, then browse the results. Three types of resources cover most needs.
- Intervention Reports summarize all the research the WWC has reviewed on a specific program or practice. If you’re evaluating whether to adopt a particular reading curriculum, the intervention report tells you how many studies were reviewed, how many met standards, and what the evidence says about effectiveness.
- Practice Guides offer evidence-based recommendations for improving student outcomes in a given area. These are written for practitioners and structured around actionable steps, not academic jargon. A practice guide on teaching writing, for example, walks through recommended strategies and rates the strength of the evidence behind each one.
- Reviews of Individual Studies give you the WWC’s assessment of a single piece of research, including whether it met standards and what the study found. This is useful when a vendor cites a specific study to promote their product and you want an independent evaluation of that study’s quality.
The WWC also offers downloadable data from its study reviews, which researchers and district evaluation teams can use for deeper analysis.
Who Runs It and How Reviews Are Conducted
The WWC is managed by IES staff and carried out under contracts with organizations that specialize in education research methodology, including Mathematica and the Instructional Research Group. The reviewers follow a published set of standards (currently version 2.1 and later) that spell out exactly how studies are assessed. This transparency is one of the clearinghouse’s key strengths: anyone can read the standards document and understand why a particular study was rated the way it was.
Because reviews take time, the WWC doesn’t cover every education product on the market. Newer programs may not yet have enough published research to be reviewed, and some programs with existing studies may not have been selected for review. A program’s absence from the WWC doesn’t mean it’s ineffective; it means the clearinghouse hasn’t evaluated the evidence yet.
Why It Matters for Schools Spending Federal Funds
For district administrators and grant writers, the WWC is more than a nice reference tool. Many federal education grants now require applicants to demonstrate that their proposed interventions meet a specific ESSA evidence tier. Citing a WWC-reviewed program with a strong or moderate evidence rating can strengthen a grant application and, in some cases, is a prerequisite for funding. Current federal priorities emphasize evidence-based programs in math and literacy, as well as interventions for students with disabilities, particularly around improving literacy for students with dyslexia and other conditions affecting reading and language processing.
Even without a federal mandate, the WWC helps schools avoid spending limited budgets on programs that sound promising but lack credible research behind them. When a sales rep claims their software “raises test scores by 20 percent,” the clearinghouse gives you a way to check whether that claim holds up under scrutiny.