If you're evaluating a curriculum or intervention, "ESSA evidence" will almost certainly come up. Vendors routinely describe products as evidence-based, but that phrase has a specific legal meaning under ESSA, and not every claim meets the standard. Understanding the evidence tiers helps you determine whether a program qualifies for your funding and whether the research behind it is stronger than the marketing.
ESSA defines four tiers of evidence: Tier 1 (Strong), Tier 2 (Moderate), Tier 3 (Promising), and Tier 4 (Demonstrates a Rationale). The first three are based on studies showing a statistically significant, positive effect; the fourth rests on a research-based rationale. Interventions paid for with Section 1003 school-improvement funds must meet Tiers 1, 2, or 3.
Why the tiers matter when you buy curriculum
Since the Every Student Succeeds Act replaced No Child Left Behind, federal law has asked schools to spend certain funds on "evidence-based" interventions, and it defines that term precisely. For a curriculum director or district administrator, that turns a research question into a procurement question. A program's evidence tier can determine whether you are allowed to buy it with a given pot of money, and it is one of the few objective signals you have about whether a product actually works.
The trouble is that "evidence-based" has become a marketing phrase as much as a legal one, and vendors use it loosely. Understanding the tiers lets you tell a real evidence claim from a hopeful one before the purchase order goes out. This guide explains each tier, which funding sources require them, and how to evaluate a vendor's evidence claim before making a purchase. (For a closer look at Tier 3 specifically, which is where many curriculum claims land, see the companion guide.)
The four tiers of evidence
ESSA doesn't leave "evidence-based" up for interpretation. The law defines four evidence tiers, each based on the type of research supporting the program. The top three are defined by the kind of study behind them, and each of those three requires the study to show a statistically significant and positive effect on a relevant outcome. The fourth is different in kind: it rests on a rationale rather than a finding.
| Tier | ESSA name | What it requires | Counts for Section 1003 school improvement? |
|---|---|---|---|
| Tier 1 | Strong | At least one well-designed, well-implemented experimental study (a randomized controlled trial) showing a significant positive effect | Yes |
| Tier 2 | Moderate | At least one well-designed, well-implemented quasi-experimental (matched) study showing a significant positive effect | Yes |
| Tier 3 | Promising | At least one well-designed, well-implemented correlational study, with statistical controls for selection bias, showing a significant positive effect | Yes |
| Tier 4 | Demonstrates a rationale | A well-specified logic model supported by research, plus an ongoing effort to study the intervention's effects | No |
The shorthand is that the tiers describe how confident you can be that the program caused the result. A randomized trial (Tier 1) gives the strongest causal claim; a matched quasi-experimental study (Tier 2) is a step down; a correlational study with controls (Tier 3) is "promising" because it shows a relationship while controlling for some bias, but cannot establish cause the way a trial can. Tier 4 is for promising ideas still building their evidence.
One technical point worth knowing: the U.S. Department of Education considers a study "well-designed and well-implemented" only if it meets the What Works Clearinghouse standards. So a vendor saying it has "a study" is not the same as having a study that meets the bar for a tier.
Which tier does your funding require?
This is the part that turns the tiers from academic to practical, and it is simpler than it looks.
Interventions paid for with Section 1003 school-improvement funds (the set-aside for the lowest-performing schools) must meet Tiers 1, 2, or 3. Tier 4 does not qualify for these funds, because a rationale alone is not enough when the stakes and the funding are aimed at turning around struggling schools.
All other programs under Titles I through IV can rely on any of the four tiers, including Tier 4.
So before you evaluate a specific product, know which money you are spending. If it is school-improvement money, a Tier 4 "demonstrates a rationale" claim, however reasonable, will not satisfy the requirement, and you need a program backed by promising, moderate, or strong evidence.
How to read a vendor's evidence claim
Most evidence problems in procurement are not outright falsehoods. They are claims that sound stronger than they are. A few checks catch most of them.
Ask which tier the vendor is claiming, in writing. "Evidence-based" with no tier is not an answer. "Research-based" is not the same as "evidence-based" under ESSA, and "aligned to the science of reading" is a description of approach, not an evidence rating.
Ask whether the study is on the product you are buying. Evidence for an earlier edition, a different grade band, or a similar-but-not-identical program does not automatically transfer. The study should be on the thing in the cart.
Ask whether the study showed a statistically significant, positive effect on a relevant outcome. For Tiers 1 through 3, that finding is the requirement, not an optional bonus. A study that found no significant effect does not establish a tier, even if it exists.
Ask whether the study meets What Works Clearinghouse standards, since that is the bar the Department of Education uses for "well-designed." Independent listings, such as the WWC itself or the Evidence for ESSA database, can confirm a rating rather than relying on the vendor's own characterization.
A note on evidence and good instruction
Meeting an ESSA tier and being good instruction are related but not identical. A tier tells you a program has cleared a research bar; it does not, by itself, tell you the program reflects the science of reading or that your teachers can deliver it well. The strongest procurement decisions check both: that a program meets the evidence requirement for the funds being used, and that it reflects structured literacy and comes with the support teachers need to put it into practice. Evidence on paper and results in classrooms are not the same thing, and the gap between them is filled by implementation.
Frequently asked questions
What are the four ESSA evidence tiers?
Tier 1 (Strong) rests on an experimental study, usually a randomized controlled trial. Tier 2 (Moderate) rests on a quasi-experimental study. Tier 3 (Promising) rests on a correlational study with controls for selection bias. Tier 4 (Demonstrates a Rationale) rests on a research-based logic model with ongoing evaluation. The top three require a statistically significant, positive effect.
Which ESSA tiers qualify for school improvement funds?
Interventions funded under Section 1003 school improvement must meet Tier 1, 2, or 3, that is, strong, moderate, or promising evidence. Tier 4 does not qualify for Section 1003 funds. All other programs under Titles I through IV can use any of the four tiers.
What is the difference between "evidence-based" and "research-based"?
"Evidence-based" has a specific legal meaning under ESSA, tied to the four tiers and to studies showing effects. "Research-based" has no such definition and often means only that a program is informed by research. For ESSA funding purposes, a vendor needs to claim a specific evidence tier, not just call itself research-based.
Does meeting an ESSA tier mean a program is high quality?
It means the program has cleared a research bar, which is meaningful, but it is not the whole picture. An evidence tier does not guarantee that a program reflects current reading research or that teachers can implement it well. Strong decisions weigh the evidence tier alongside instructional design and the support that comes with the program.
How can I verify a vendor's ESSA tier claim?
Ask for the specific tier and the study behind it, confirm the study is on the product you are buying, and check independent sources such as the What Works Clearinghouse or the Evidence for ESSA database rather than relying solely on the vendor's own description.
Keep reading
- What does ESSA Tier III evidence actually require?
- What is structured literacy?
- What is the science of reading? A guide for school leaders
- What science of reading professional development should include
- Literacy leadership development
ESSA's four evidence tiers and the requirement that Section 1003 school-improvement interventions meet Tiers 1–3 are defined in the Every Student Succeeds Act (ESEA as amended, § 8101(21)) and U.S. Department of Education guidance. Study-quality determinations reference the What Works Clearinghouse standards.
