The aim of this study was to clarify the reason for differences between bone-conduction hearing in adults and infants. The authors investigated how the sound pressure level in the ear canal changes depending on the bone-conduction transducer placement. By using in the ear sound pressure measurement authors tried to investigate how developing skull properties influence the attenuation. Transcranial and forehead attenuation was estimated for 59 children including infants and for seven adults as a difference between sound pressures in the ear canal when the transducer was placed at the ipsilateral temporal bone and at the contralateral temporal bone or forehead. Measurements were collected for four frequencies that the bone conduction thresholds are usually measured at during a pure tone audiometry test. Results were compared between five age groups including children. Similar to previous studies, the bone-conduction attenuation was more prominent in infants than in adults. However, there was no significant interaction between age group and frequency. The BC attenuation was different for different frequencies and was greatest for 1 kHz. However, authors indicated that the differences in middle ear properties and condition between adults and children may be a confounding factor. In general, this study’s results support previous findings which may have an effect on BHAS fitting recommendation.