Online mathematics instruction has been growing significantly between 2013 and 2023 due to the development of digital solutions and a sudden shift to distance learning caused by the COVID-19 pandemic [5], [24]. The current article is an extensive synthesis of 41 empirical works, thus, mapping the benefits, challenges and effective design practices in K-12 and higher education environments. Among the benefits reported are flexibility of access, interactive resources, community scaffolds that promote engagement and persistence [3], [15], [25], persistent barriers as experienced by learners and teachers are reported as unequal access, motivation, integrity of assessment, and workload strain [14], [19], [24], [27], [28]. Positive outcomes of mathematics proficiency, self-efficacy, and discourse have been shown with pedagogical models of flipped classroom and communities of inquiry when they are designed purposely with feedback and structure [7], [35]. The domain-specific affordances are created in the context of modelling and problem-solving activities where digital tools allow visualisation, iteration, and collaboration, but also create orchestration complexity at the same time [18], [41]. The acceptance and knowledge practices are affected by social and media ecosystems, posing the idea that the characteristics of the platform and its norms contribute to the adoption of e-learning in mathematics settings [1], [6], [11]. Theoretically, the corpus is biased in terms of cross-sectional surveys and case studies and few longitudinal or experimental designs, so reflexive thematic analysis has been used to combine results and surface design principles and gaps in the research [17], [29]. The review suggests (i) the structured interaction as opposed to discussion boards [22]; (ii) the evaluation designs that are aligned to mathematical reasoning as opposed to simple recall [33], [40]; (iii) the teacher development that is geared towards the alignment of the technology with the pedagogy and ensuring equitable participation [30], [34]. These have implications on curriculum design, platform choice, and policy geared towards a continuation of inclusive online mathematics learning.