The Home Learning Environment (HLE) focuses on everyday learning habits in families to support the development of children's early cognitive competencies. A growing number of studies have assessed the HLE by using different conceptual approaches and various assessment methods, often focusing on either the home literacy environment or the home numeracy environment. However, it is still unclear whether the 2 dimensions of the HLE are separable constructs and which assessment method is best suited for assessing the HLE, making it difficult to interpret and compare different study results. In the current study, we used multitrait-multimethod (MTMM) analyses to compare 3 common methods for assessing the HLE and their relations to various outcomes of kindergarten children. Our sample consisted of 2 independent cohorts of children (N[subscript 1] = 190, N[subscript 2] = 310) with an average age of 61 months (SD = 4.6). In both cohorts, the MTMM matrix showed a substantial effect of common methods and indicated a 1-dimensional HLE construct indicated most strongly by the children's book title recognition test (TRT-VS). Even when controlling for child and family characteristics (i.e., intelligence and socioeconomic status), the HLE was statistically significantly related to both the mathematical competencies and the linguistic competencies of the child in a structural equation model. This pattern of results was found consistently across both cohorts. We discuss the significance of a 1-dimensional HLE construct and its different assessment methods in the light of implications for future research and interventional approaches.