Background: Language interventions are complex behavioural interventions, making it difficult to distinguish the specific factors contributing to efficacy. The efficacy of oral language comprehension interventions varies greatly, but the reasons for this have received little attention. Aims: The aim of this meta-analysis was to examine which intervention factors are associated with efficacy (as expressed with effect sizes) regarding interventions aiming to improve oral language comprehension on its own, or together with expressive language, in children under the age of 18 with or at risk for (developmental) language disorder--(D)LD. Whether the interventions for younger and older children differ from one another regarding efficacy or factors possibly associated with efficacy were also examined. Methods & Procedures: Studies (n = 46) were identified through two systematic scoping reviews. Factors associated with efficacy were categorized according to the internal characteristics of the intervention as well as factors external to the intervention. Statistical analyses were conducted to examine the association between these factors and intervention efficacy as represented by effect sizes on oral language comprehension outcome measures. Outcomes & Results: Targeting language, language environment or compensatory strategies indicated efficacy, whereas aiming to improve language processing indicated no clinically significant efficacy. Targeting only receptive language was associated with larger effect sizes than targeting both receptive and expressive language. The interventions for younger (2-7 years) and older (8-13 years) children indicated a similar degree of efficacy, but the way in which these results were achieved varied, as comprehension interventions for younger and older children differed from one another. Many factors associated with effect sizes were also associated with each other making interpretation of the results complex. Conclusions & Implications: These indicative results suggest that it is not reasonable to target language processing, such as auditory processing or automatization, when aiming to improve oral language comprehension. Targeting receptive language only rather than both receptive and expressive language seems preferable to maximize efficacy when aiming to support solely oral language comprehension instead of targeting both expression and comprehension. The qualitative active ingredients of treatment appear to be more important than the number of intervention hours. Although children of different ages can benefit from interventions to enhance oral language comprehension, the child's age needs to be carefully considered to develop interventions that are optimal. Further research with larger data sets regarding factors contributing to efficacy is still needed before applying these results confidently to clinical practice.