This report has two main purposes. First, we combine well-known analytical approaches to conduct a comprehensive assessment of agreement and correlation of rating-pairs and to dis-entangle these often confused concepts, providing a best-practice example on concrete data and a tutorial for future reference. Second, we explore whether a screening questionnaire developed for use with parents can be reliably employed with daycare teachers when assessing early expressive vocabulary. A total of 53 vocabulary rating pairs (34 parent–teacher and 19 mother–father pairs) collected for two-year-old children (12 bilingual) are evaluated. First, inter-rater reliability both within and across subgroups is assessed using the intra-class correlation coefficient (ICC). Next, based on this analysis of reliability and on the test-retest reliability of the employed tool, inter-rater agreement is analyzed, magnitude and direction of rating differences are considered. Finally, Pearson correlation coefficients of standardized vocabulary scores are calculated and compared across subgroups. The results underline the necessity to distinguish between reliability measures, agreement and correlation. They also demonstrate the impact of the employed reliability on agreement evaluations. This study provides evidence that parent–teacher ratings of children's early vocabulary can achieve agreement and correlation comparable to those of mother–father ratings on the assessed vocabulary scale. Bilingualism of the evaluated child decreased the likelihood of raters' agreement. We conclude that future reports of agreement, correlation and reliability of ratings will benefit from better definition of terms and stricter methodological approaches. The methodological tutorial provided here holds the potential to increase comparability across empirical reports and can help improve research practices and knowledge transfer to educational and therapeutic settings.

This study investigates the predictive value of child-related and environmental characteristics for early lexical development. The German productive vocabulary of 51 2-year-olds (27 girls), assessed via parental report, was analyzed taking children’s gender, the type of early care they experienced, and their mono- versus bilingual language composition into consideration. The children were from an educationally homogeneous group of families and state-regulated daycare facilities with high structural quality. All investigated subgroups exhibited German vocabulary size within the expected normative range. Gender differences in vocabulary composition, but not in size, were observed. There were no general differences in vocabulary size or composition between the 2 care groups. An interaction between the predictors gender and care arrangement showed that girls without regular daycare experience before the age of 2 years had a somewhat larger vocabulary than all other investigated subgroups of children. The vocabulary size of the 2-year-old children in daycare correlated positively with the duration of their daycare experience prior to testing. The small subgroup of bilingual children investigated exhibited slightly lower but still normative German expressive vocabulary size and a different vocabulary composition compared to the monolingual children. This study expands current knowledge about relevant predictors of early vocabulary. It shows that in the absence of educational disadvantages the duration of early daycare experience of high structural quality is positively associated with vocabulary size but also points to the fact that environmental characteristics, such as type of care, might affect boys’ and girls’ early vocabulary in different ways.