To examine the difference in the rehabilitation rate from underweight by child age at enrolment in the Positive Deviance (PD)/Hearth programme.

This secondary data analysis used programme monitoring records of underweight children aged 6–60 months attending a 2-week PD/Hearth session and followed up for 6 months from September 2018 to March 2019. Data were analysed using multilevel mixed-effect regression and Poisson regression with robust variance.

Rajshahi Division, Bangladesh.

A total of 5227 underweight (weight-for-age Z-score (WAZ) <-2) children attended the PD/Hearth sessions.

From enrolment to 6 months follow-up, the mean WAZ improved from −2·80 to −2·09, and the percentage of underweight children decreased to 54·5 %. Compared to the enrolment age of 6–11 months, the estimated monthly change in WAZ at 6 months of follow-up were 0·05 lower for 12–23 months, 0·06 lower for 24–35 months, and 0·09 lower for 36–60 months of the enrolment age (all P < 0·001). The probability of rehabilitation at 6 months of follow-up were lower by 16·7 % for 12–23 months (RR = 0·83; 95 % CI 0·77, 0·91), 15·5 % for 24–35 months (RR = 0·84; 95 % CI 0·78, 0·92), and 34·9 % for 36–60 months of the enrolment age (RR = 0·65; 95 % CI 0·59, 0·72), compared to the enrolment age of 6–11 months.

Enrolment in the PD/Hearth programme at a younger age had the advantage of greater rehabilitation from underweight than older age. Our findings provide a better understanding of the successes and failures of the PD/Hearth programme to achieve more sustainable and cost-effective impacts.