Good quality of voice signal and adequate classroom acoustics are important factors to guarantee an optimal teaching-learning process. This systematic review aims to characterize the relationship between intelligibility of the speech and room acoustics in primary schools based on the available evidence. Eligible studies were identified using two computerized databases: PubMed and Scopus. In total, 21 publications met our inclusion criteria: (1) subjects must have been from primary schools; (2) acoustic characterization of the classroom must been provided; (3) intelligibility tests must have been performed; and (4) articles written in English. After identifying the parameters and tests used to define the intelligibility of the speech, the subjective scores were analyzed in relationship with voice related parameters found in the articles (SNR and STI). Our results highlight the negative effect on intelligibility associated with the bad transmission of the speech and a poor acoustic of the classroom caused by long reverberation times and high background noise. Future research needs to include stronger study designs than “one-time survey” and analyze the results even in cases of acoustic interventions.