Explore the evidence
7 of 88 decisions · clear everything
Later bells buy adolescents 40+ measured minutes of sleep — the best-identified positive effect in the archive; the achievement payoff is real but far smaller.
strong supportconf: mediumgc: lowDo later school start times increase adolescent sleep, and does that raise achievement? · health · ages 11–18 · input
Diagnose what a child already knows: teachers cut 40–50% of curriculum for high-ability children and achievement ROSE. The payoff is skipping, not monitoring.
moderate supportconf: mediumgc: mediumPlacement and mastery diagnosis — deciding what to teach next from evidence of current skill · assessment · ages 5–18 · structure
The received wisdom that retention is harmful was two measurement errors, not a finding. Fix them and the achievement effect is zero — but the grade at which you hold a child back decides everything.
mixedconf: mediumgc: lowGrade retention — holding a child back versus promoting, and test-based promotion policies · retention · ages 5–18 · structure
Classroom order is causally worth a great deal — one disruptive peer costs classmates 3% of adult earnings — yet no branded behaviour programme reliably delivers it and exclusion makes things worse.
mixedconf: mediumgc: lowHow should a school run its classrooms and its discipline system? · behavior · ages 4–18 · structure
Taking time away hurts measurably; adding it back buys almost nothing. The return per hour is ~0.02-0.03 SD, concave, and near zero in disorderly classrooms.
mixedconf: mediumgc: lowLength of the school day and year, time-on-task, extended time, and summer · time · ages 4–18 · structure
Coaching buys ~0.25 SD of score and has for 42 years — a fraction of what's advertised — and none of it is ability. The score moves; the construct doesn't.
mixedconf: mediumgc: mediumTest preparation — does coaching raise scores, and does a raised score mean raised ability? · assessment · ages 5–18 · structure
No study of homeschooling has a counterfactual — the famous percentile claims are selection all the way down. The honest answer: nobody knows.
insufficientconf: lowgc: highDoes homeschooling raise achievement and attainment, or does it select the children who would have done well anyway? · homeschool · ages 5–18 · structure
- Acceleration and gifted programs — the label vs the content
- Chronic absenteeism — does raising attendance raise achievement?
- Class-size reduction
- Curriculum choice as a school-level lever
- Physical activity as an input — dose, fitness, and school outcomes
- Fadeout — why early gains disappear, and what actually persists
- Ability grouping and tracking — four practices, four verdicts
- The early home environment — what parents can and cannot causally move
- Homeschool socialisation — the most-asked question, and the least answerable one
- Breakfast, school meals, and micronutrients — what feeding children actually buys
- Preschool at scale — Head Start, state pre-K, and what universal provision delivers
- Perry Preschool and Abecedarian — what the famous studies actually establish
- School spending, charters, and what school-level choices actually move outcomes
- School starting age, relative age, and academic redshirting
- Talent and trainability — what is heritable, and what that does not license
- Teacher quality — selection over credentials and workshops
- Vision — outdoor time against myopia, and screening and correction for achievement
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