Evidence file: fractions on the number line

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
Fuchs et al. 2013(opens in a new tab)	Randomized trial	About 290 at-risk 4th graders (Blueprints(opens in a new tab))	School's usual fraction teaching	Better on fraction comparison, number line, calculations, and released NAEP items	At-risk students only
Fuchs et al. 2014(opens in a new tab)	Randomized trial	277 at-risk 4th graders, 49 classrooms, 14 schools	Usual teaching	Gains on NAEP fraction items and number line	Researcher-developed program
Fuchs et al. 2016(opens in a new tab)	Randomized trial	213 at-risk 4th graders	Usual teaching	Better understanding and calculation; NAEP gains explained by better fraction-size understanding	Small groups, not whole class
Malone et al. 2019(opens in a new tab)	Randomized trial	225 at-risk 4th graders	Usual teaching	Gains transferred to decimals without decimal instruction	Same research group
Fuchs et al. 2017 review(opens in a new tab)	Summary of five trials	At-risk 4th graders	—	Consistent effects across five years of trials	Same research group
Siegler et al. 2012(opens in a new tab)	Correlation, longitudinal	U.S. and U.K. students	—	5th grade fraction knowledge predicted high school algebra	Not causal

Cautions

All five trials come from one research group, testing its own program with at-risk 4th graders in small groups. That is strong evidence for that use, and a reasonable but untested basis for whole-class number-line teaching.
The fractions practice guide rated its recommendation on early sharing activities as minimal evidence (Marzano summary of Rec. 1(opens in a new tab)), so not every popular fraction activity is backed equally.