The core symptom of the anxiety disorder selective mutism (SM) is absence of speech in specific situations, such as at school. The most commonly used standardized instruments to assess speaking behavior are the parent-rated Selective Mutism Questionnaire (SMQ) and the teacher-rated School Speech Questionnaire (SSQ), scored from 0 to 3, indicating that speaking behavior never, seldom, often, and always occur. They were developed to assess severity of mutism and potential effects of treatment. However, prospective data on speaking behavior in typically developing children (TDs) are missing in the literature. The main aim of this study was to present data from TDs over time with previously reported data from children treated for SM, as a comparison. Participants were 64 children aged 3–9 years, 32 TDs who were a matched control group to 32 children with SM. At baseline, the mean SMQ and SSQ scores were ⩾2.5 in TDs and 0.5 in children with SM. The TDs did not show significant changes over time, while significantly increased speech was found in children with SM after treatment. Thus, our findings support the use of the SMQ/SSQ to assess baseline SM severity and to evaluate potential treatment effects in future studies.