C23 weakened
For teenage and adult second-language learners, spreading vocabulary practice out instead of massing it gives clearly better results on tests a day or more later (g = 1.15 in a meta-analysis of controlled studies); for grammar this delayed advantage has not been shown (g = 0.11, not significant). Longer gaps have beaten shorter ones on delayed tests when the gaps fall within one session and in adults, but between separate sessions longer gaps have not been shown to add a reliable benefit (Kim & Webb 2022).
Bounds: Second-language vocabulary, grammar and pronunciation practice in controlled studies, with delayed tests; not classroom-wide year-long durability (see C11 for spacing in general). Evidence on file: Kim & Webb 2022 (Language Learning 72(1), 269–319, DOI 10.1111/lang.12479; full text supplied by Jonatan 2026-11-04, read 2026-11-05): 48 experiments from 37 studies, 98 effect sizes, N = 3,411. Spaced vs massed: immediate g = 0.58 (95% CI 0.16 to 1.00; k = 11); delayed g = 0.80 (0.44 to 1.17; k = 15; I² = 82%; prediction interval −0.64 to 2.24). On delayed tests by learning target: vocabulary g = 1.15 (0.81 to 1.49; k = 10), grammar g = 0.11 (−0.32 to 0.54; k = 5), difference Q = 13.78, p < .001; adults 0.77 (k = 12), school-age learners (grades 1–12) 0.97 (k = 3). Longer vs shorter spacing: immediate g = −0.15 (ns; k = 17); delayed g = 0.40 (0.16 to 0.64; k = 32). On delayed tests: adults (university students or older) 0.54 (0.27 to 0.81; k = 24) vs school-age learners −0.04 (−0.52 to 0.44; k = 8), Q = 4.35, p = .04; spacing within one session 0.76 (0.42 to 1.11; k = 11) vs between separate sessions 0.18 (−0.10 to 0.45; k = 21), Q = 6.83, p = .01; grammar 0.56 (0.06 to 1.06; k = 8), vocabulary 0.34 (0.04 to 0.64; k = 22). Equal vs expanding spacing: no reliable difference. Publication bias: apparent in the delayed spaced-vs-massed subset; p-uniform judged it negligible, but the authors could not rule bias out and say true effects may be smaller. Few studies with school-age learners (3 spaced-vs-massed, 8 longer-vs-shorter effects); the claim says 'teenage' because the meta-analysis pools all school ages. Nakata 2015 (Studies in Second Language Acquisition, DOI 10.1017/S0272263114000825; abstract only): 128 Japanese college students, 20 word pairs; the amount of spacing had large effects; expanding spacing a small edge over equal spacing. Between-session gaps for grammar: open question 20 (Suzuki 2017; Suzuki & DeKeyser 2017).
Attack record: 1 attack: 1 narrowed · Evidence links: 5 linked sources (1 supports, 4 limits)