Objective: Our interest was in how teachers’ voices behave during the delivery of lessons in core subjects (e.g., mathematics, science, etc.). We sought to evaluate the relationship between voice sound pressure level (SPL), vocal fundamental frequency (F₀), voice symptoms, activity noise, and differences therein during the first and the last lessons in core subjects of the day. Patients and Methods: The participants were 24 female elementary school teachers. Voice symptoms were evaluated by questionnaire. The data were recorded on 2 portable voice accumulators (VoxLog) from the first and last lessons of the day. The versions of accumulators differed by frequency weighting; therefore, the analysis and the results of noise and voice SPL were treated separately: unweighted (group 1) and A-weighted (group 2). Results: Difference in voice SPL followed difference in activity noise. F₀ increased between the first and last lessons. Correlations were found between differences in the noise and the voice symptoms of tiredness and dryness. Irritating mucus was associated with high F₀ during the first lesson. Conclusion: An apparent increase in voice loading due to the activity noise was observed during lessons in core subjects. Collaboration between specialists in voice and acoustics and teachers and pupils is needed to reduce this voice loading.