Concept Development [CD] in the early years cannot be complete without teachers' support. However, limited research exists. This research aimed to assess CD classroom interactional quality and its relationship with other quality dimensions/domains and children's overall development using the data collected in State Pre-K/Head Start classrooms with Pre-K CLASS and LAP-3. Data collected from 171 classrooms underwent analysis with Python and SPSS. Pre-K CLASS scores showed that with the exception of one high-quality classroom, all other classrooms were categorized as either mid-quality or low-quality CD. Moreover, most teachers showed lower interactional quality not only in the CD dimension but also in the Quality of Feedback [QF] and Language Modeling [LM] dimensions of Instructional Support [IS], than in the dimensions of Emotional Support [ES] and Classroom Organization [CO] domains. The results indicated that CD, QF, and LM quality dimensions did not differ across the classrooms or districts. However, ES, CO, and IS domains differed significantly. While the observed differences for ES and CO were similar between the two districts, District 1 had higher mean IS scores than District 2. Furthermore, LAP-3 scores of 2514 children showed that 26.7 % of children scored below the expected level in cognitive development and 35.5 % scored below in language development by the end of the school year, with a higher proportion of male children falling in this category. Nonetheless, children attending State Pre-K/Head Start classrooms demonstrated an average gain of 4 months beyond their chronological age. The multi-level regression analysis of Pre-K CLASS and those LAP-3 scores showed no statistically significant relationship between interactional quality and children's developmental progress. Children in mid-quality CD classrooms showed slightly more progress in all areas of development, except in personal/social, compared to children in low-quality CD classrooms. Similarly, children in mid-quality IS classrooms outperformed those in low-quality IS classrooms in all LAP-3 areas except personal/social and pre-writing as well. In conclusion, the current research suggests that many teachers struggle not only to effectively provide high-quality CD teacher-child interactions but also high-quality IS teacher-child interactions in their classrooms. Comprehensive in-service training on CD and an alternative assessment tool that extends beyond the 72-month age limit are strongly recommended. This is important to ensure that teachers are equipped with the necessary skills and motivation to provide high-quality education to young children to prevent developmental delays in children. (author abstract)