The current project longitudinally investigated the extent to which first-year Japanese university students developed their second language (L2) oral ability in relation to increased input in foreign language classrooms. Their spontaneous speech was elicited at the beginning, middle and end of one academic year, and then judged by linguistically trained coders for pronunciation, fluency, vocabulary and grammar qualities. According to the statistical analyses, the total amount of input (operationalized as number of English classes taken and L2 use outside of classrooms) was significantly related to the participants’ quick and immediate development of fluency and lexicogrammar during the first semester. Their pronunciation development was mixed, either subject to continuous change over two academic semesters (for prosody) or limited within the timeframe of the study (for segmentals). Similar to naturalistic L2 speech learning, the findings support the multifaceted role of input in different areas of oral proficiency development in foreign language classrooms.