**Paper**: "Docosahexaenoic acid for reading, working memory and behavior in UK children aged 7-9: A randomized controlled trial for replication (the DOLAB II study)" available at: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192909 **PROTOCOL**: detailed study protocol available at: dx.doi.org/10.17504/protocols.io.k8kczuw . **BACKGROUND**: Omega-3 fatty acids are central to brain-development of children. Evidence from clinical trials and systematic reviews demonstrates the potential of long-chain Omega-3 supplementation for learning and behavior. However, findings are inconclusive and in need of robust replication studies since such work is lacking. **OBJECTIVES**: Replication of the 2012 DOLAB 1 study findings that a dietary supplementation with the long-chain omega-3 docosahexaenoic acid (DHA) on the reading, working memory, and behavior of healthy schoolchildren from the 2012 DOLAB 1 study. **DESIGN**: Parallel group, fixed-dose, randomized, double-blind, placebo-controlled trial (RCT). **SETTING**: Mainstream primary schools (n=76) from five counties in the UK (n=76) in 2012-2015. **PARTICIPANTS**: Healthy children aged 7-9 underperforming in reading (<20th centile). 1230 invited, 376 met study criteria. **INTERVENTION**: 600 mg/day DHA (from algal oil), placebo: taste/color matched corn/soybean oil; for 16 weeks. **MAIN OUTCOME MEASURES**: Age-standardized measures of reading, working memory, and behavior, parent-rated and as secondary outcome teacher-rated. **RESULTS**: 376 children were randomized. Reading, working memory, and behavior change scores showed no consistent differences between intervention and placebo group. Some behavioral subscales showed minor group differences. In both treatment groups behavior improved slightly. **CONCLUSIONS**: This RCT did not replicate results of the earlier DOLAB 1 study on the effectiveness of nutritional supplementation with DHA for learning and behavior. Possible reasons are discussed, particularly regarding the replication of complex interventions. **REGISTRATION:** The trial was pre-registered at: [www.controlled-trials.com][1] (ISRCTN48803273) **AUTHORS**: The Study was conceived by [Dr Alex J Richardson][2] and [Prof Paul Montgomery][3], run by Ms Jennifer Burton, Ms Alice Burton, and Dr Thees Spreckelsen. **FUNDING:** The study was funded by [DSM Nutritional Products][4]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. **Ethical consent** was gained from the [Oxford B NHS Ethics Board][5], 15/10/2012, ref:12/SC/0465. [1]: http://www.controlled-trials.com [2]: https://www.fabresearch.org/viewItem.php?id=7412 [3]: http://www.birmingham.ac.uk/schools/social-policy/staff/profile.aspx?ReferenceId=129385 [4]: http://www.lifesdha.com/ [5]: http://www.hra.nhs.uk/news/rec/south-central-oxford-b/