Evidence file: the curriculum you choose

Study label	Meaning
Randomized trial	Students, classes, or schools assigned by chance. The strongest single-study design.
Lottery study	Admission by lottery, which works like random assignment for those who applied.
Meta-analysis	A combined analysis of many studies; only as strong as the studies inside it.
Comparison study	Groups compared without random assignment. Useful, but differences may come from who chose what.
Lab study	Controlled experiment outside a regular classroom. Explains why; doesn't prove it works at scale.
Correlation	Two things move together. Shows a link, never cause. Used only for "why it matters."

Study label

Meaning

Randomized trial

Students, classes, or schools assigned by chance. The strongest single-study design.

Lottery study

Admission by lottery, which works like random assignment for those who applied.

Meta-analysis

A combined analysis of many studies; only as strong as the studies inside it.

Comparison study

Groups compared without random assignment. Useful, but differences may come from who chose what.

Lab study

Controlled experiment outside a regular classroom. Explains why; doesn't prove it works at scale.

Correlation

Two things move together. Shows a link, never cause. Used only for "why it matters."

Study	Design	Who	Compared with	Found	Limits
Agodini et al. 2010–2013(opens in a new tab)	Randomized trial, curricula assigned to schools	110 elementary schools, 12 districts, grades 1–2, disadvantaged schools	Four curricula against each other	Math Expressions, Saxon, and SFAW/enVision all outperformed Investigations by end of grade 2	Early grades; older editions
Jackson & Makarin 2018(opens in a new tab)	Randomized trial	363 teachers, about 27,600 middle school students, Virginia	No license or support	Lessons plus support: +0.086 SD; lessons alone: smaller, not consistently significant	Inquiry-oriented lessons, so not a test of explicit vs inquiry
Blazar et al. 2020(opens in a new tab)	Comparison study across six states	Nearly 6,000 schools, grades 4–5	Schools using other textbooks	Little difference in average math gains by textbook; more variation where texts were used more	Not randomized; low PD and partial use (CEPR(opens in a new tab))

Reading the evidence honestly

The one large randomized trial of elementary curricula found real differences, favoring programs with more structure over the most student-centered one.
The largest non-random study found textbook choice alone made little difference at typical levels of use and training.
Both point the same way for a district: pick strong materials and fund the training and visits that get them used as designed.