This study examines the impact of early childcare teachers’ professional development (PD) training in global and domain-specific interaction quality and its effects on children’s numeracy skills and mathematical language development. Previous studies have highlighted the importance of high-quality interactions, using tools like dialogic reading and playing board games, in promoting young children’s numeracy skills and their mathematical language. However, few studies investigated the importance of the specificity of the training by offering a training in math-specific as well as a training in global interaction quality. Moreover, existing studies have primarily focused on children aged three years and older, despite the importance of early intervention. To address these gaps, this study integrated promising interaction strategies into PD training for early childcare teachers working with toddlers. It evaluated the short- and long-term effectiveness of this training on numeracy skills and mathematical language in children aged two to four. Two intervention groups received either math-specific or global interaction quality training, while a control group received no training. Results showed significant improvements in numeracy skills and mathematical language over time, with stronger effects observed in the math-specific intervention group compared to the control group. The global intervention group showed stronger effects in language competencies compared to the control group. These findings underscore the effectiveness of targeted PD training in fostering children’s early numeracy skills and mathematical language. By systematically varying intervention content and controlling for environmental factors, this study provides valuable insights into the specific benefits of math-specific training for early childcare teachers.