Soil transmitted (or intestinal) helminths and schistosomes affect millions of children worldwide. There are four species of soil transmitted helminths: "Ascaris lumbricoides" (roundworm), "Necator americanus" and "Ancylostoma duodenale" (hookworms), and "Trichuris trichura" (whipworm). The five species of schistosomes which affect humans include: "Schistosoma (S.) mansoni," "Schistosoma japonicum," "Schistosoma mekongi," "Schistosoma intercalatum" (which cause intestinal schistosomiasis) and "Schistosoma haematobium" (which causes urinary schistosomiasis). Mass deworming is applied widely to reduce the consequences of helminth infection, and there have been numerous studies on the effects of deworming on growth, cognition and learning outcomes in children over the past several decades. Systematic reviews and meta-analyses based on aggregate results of the effect of mass deworming on health and education outcomes are conflicting with some showing benefit (Hall, Hewitt et al. 2008; Croke, Hicks et al. 2016) and others not (Taylor-Robinson, Maayan et al. 2015; Welch, Ghogomu et al. 2017). Debate has ensued about whether these conflicting results are due to the influence of variations in effect across individual-level characteristics such as whether children are infected or not and intensity of infection (Hotez, Molyneux et al. 2007; Bundy, Kremer et al. 2009; Montresor, Addiss et al. 2015) as well as setting characteristics such as the sanitation environment and rapidity of reinfection (Campbell, Nery et al.). This meta-analysis will explore the question of whether mass deworming is more effective for subgroups of children defined by characteristics such as infection intensity or status, age or nutritional status. This understanding could help to develop targeted strategies to reach these children better with deworming and guide policy regarding deworming. [The following advisory group members co-authored this article: Robert Black, Celia Holland, Deirdre Hollingsworth, Sue Horton, and Sanjay Wijeseker.]