Low socioeconomic populations, when compared to more affluent groups, are at greater risk of initiating risky behaviours and consequently developing health complications. Health literacy has been identified as a possible means to improve and sustain positive health behaviours, with adolescence being a time point when such behaviours can be embedded. To develop a meaningful health intervention, it has been recommended that relevant stakeholders be included in the design phase. This formative evaluation study was the second phase of co-design of an engaging health literacy intervention ‘LifeLab’ with, and for, socioeconomically disadvantaged adolescents in Ireland. In Spring 2021, a series of co-design workshops (n = 17) were facilitated with a convenience sample of adolescents from socially disadvantaged areas (n = 22) to gather their perceptions, feedback, and suggested changes on the LifeLab learning activities that had emerged from Phase 1 of the work. The data was analysed using reflexive thematic analysis, resulting in the development of three themes: (i) preferred learning engagement strategies, (ii) practical and logistical considerations and Citation: Smith, C.; Goss, H.R.; Issartel, J.; Meegan, S.; Belton, S. LifeLab: Co-Design of an Interactive Health Literacy Intervention for Socioeconomically Disadvantaged Adolescents’. Children 2022, 9, 1230. https://doi.org/10.3390/ children9081230 Academic Editor: Charles N. Oberg Received: 1 July 2022 Accepted: 10 August 2022 Published: 15 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). (iii) ideas for LifeLab content. The results highlight the value in adopting a participatory approach, as participants offered an array of suggestions and details to maximise the potential for LifeLab to be contextually relevant and engaging; suggestions which will directly inform the development and implementation of the intervention.