In Early Head Start (EHS), teacher-child interactions are widely believed to shape infant-toddler outcomes, yet large-scale studies often find only modest or null associations. This study addresses four methodological sources of attenuation -- item-level measurement error, center-level confounding, teacher- and classroom-level covariate imbalance, and overlooked nonlinearities -- to clarify classroom process quality's true influence on child development. Using data from the 2018 wave of the Early Head Start Family and Child Experiences Survey (Baby FACES), we applied a three-level generalized additive latent and mixed model (GALAMM) to distinguish genuine classroom-level variability in process quality, as measured by the Classroom Assessment Scoring System (CLASS) and Quality of Caregiver-Child Interactions for Infants and Toddlers (QCIT), from item-level noise and center-level effects. We then estimated dose-response relationships with children's language and socioemotional outcomes, employing covariate balancing weights and generalized additive models. Results show that nearly half of each item's variance reflects classroom-level processes, with the remainder tied to measurement error or center-wide influences, masking true classroom effects. After correcting for these biases, domain-focused dose-response analyses reveal robust linear associations between cognitive/language supports and children's English communicative skills, while emotional-behavioral supports better predict social-emotional competence. Some domains display plateaus when pushed to extremes, underscoring potential nonlinearities. These findings challenge the "null effect" narrative, demonstrating that rigorous methodology can uncover the critical, domain-specific impacts of teacher-child interaction quality, offering clearer guidance for targeted professional development and policy in EHS.

翻译：在早期启蒙计划（EHS）中，师生互动被普遍认为对婴幼儿发展具有塑造作用，但大规模研究往往仅发现微弱或零关联。本研究针对四个导致效应衰减的方法学因素——项目级测量误差、中心级混杂效应、教师与班级层面协变量失衡以及被忽视的非线性关系——以厘清课堂过程质量对儿童发展的真实影响。基于2018年度早期启蒙计划家庭与儿童经历调查（Baby FACES）数据，我们采用三层广义可加潜变量混合模型（GALAMM），以课堂评估评分系统（CLASS）和婴幼儿照护者-儿童互动质量量表（QCIT）为测量工具，将过程质量中真实的班级层面变异与项目级噪声及中心级效应进行分离。随后，我们运用协变量平衡权重与广义可加模型，估计了与儿童语言及社会情感发展成果的剂量-反应关系。结果显示：每个测量项目近半数的方差反映班级层面的过程质量，其余部分则与测量误差或中心层面影响相关，从而掩盖了真实的班级效应。校正这些偏差后，聚焦特定领域的剂量-反应分析表明：认知/语言支持与儿童英语沟通技能存在稳健的线性关联，而情感行为支持更能预测社会情感能力。部分支持领域在达到极端水平时呈现平台效应，揭示了潜在的非线性关系。这些发现挑战了“零效应”的主流论述，证明严谨的方法学能够揭示师生互动质量在特定领域的关键影响，为EHS中针对性专业发展与政策制定提供了更清晰的指导。