Background Water, sanitation and hygiene (WASH) interventions in schools may improve the health and school attendance of schoolchildren, particularly among post-menarcheal girls, but existing evidence is mixed. We examined the impact of an urban WASH in schools programme (Project WISE) on child health and attendance. Methods The WISE cluster-randomised trial, conducted in 60 public primary schools in Addis Ababa, Ethiopia over one academic year, enrolled 2-4 randomly selected classes per school (approximately 100 pupils) from grades 2-8 (aged 7-16) in an 'open cohort'. Schools were assigned 1:1 by stratified randomisation to receive the intervention during the 2021/22 academic year or the 2022/23 academic year (waitlist control). Masking was not possible. The intervention included improvements to drinking water storage, filtration and access, alongside handwashing stations and behaviour change promotion. Planned improvements to sanitation facilities were not realised. At four unannounced classroom visits between March and June 2022 (post-intervention, approximately every four weeks), enumerators recorded primary outcomes of roll-call absence, and pupil-reported respiratory illness and diarrhoea in the past seven days among pupils present. Analysis was by intention-to-treat. This study is registered with ClinicalTrials.gov, number NCT05024890. Findings Of 83 eligible schools, 60 were randomly selected and assigned. In total, 6229 eligible pupils were enrolled (median per school 101.5; IQR 94-112), with 5987 enrolled at study initiation (23rd November-22nd December 2021) and the remaining 242 during follow-up. Data were available on roll-call absence for 6166 pupils (99.0%), and on pupil-reported illness for 6145 pupils (98.6%). We observed a 16% relative reduction in the odds of pupil-reported respiratory illness in the past seven days during follow-up in intervention schools vs. control schools (aOR 0.84; 95% CI 0.71-1.00; p=0.046). No effect was observed on pupil-reported diarrhoea in the past seven days (aOR 1.15; 95% CI 0.84-1.59; p=0.39) nor roll-call absence (aOR 1.07; 95% 0.83-1.38; p=0.59). There was a small increase in menstrual care self-efficacy (aMD 3.32 on 0-100 scale; 95% CI 0.05-6.59), and no effects on the other health, wellbeing and absence secondary outcomes. Interpretation This large-scale intervention to improve WASH conditions in schools across a large city had a borderline impact on respiratory illness among schoolchildren but no effect on diarrhoeal disease nor pupil absence. Future research should establish the relationships between WASH-related illness and absence and other downstream educational outcomes. Funding Children's Investment Fund Foundation.

The authors have declared no competing interest.

NCT05024890

https://doi.org/10.6084/m9.figshare.22194298

This study was funded by the Children's Investment Fund Foundation.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The London School of Hygiene & Tropical Medicine Research Ethics Committee (reference 17761), and the National Research Ethics Review Committee of Ethiopia (NRERC; reference A/A/H/10H02/227) gave ethical approval for this work.

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All data produced in the present study will be made available in the London School of Hygiene & Tropical Medicine's Data Repository (https://datacompass.lshtm.ac.uk) with publication.