The purpose of this project was to make a preliminary investigation of the processes of second language acquisition by children, adolescents and adults, and to develop a methodology appropriate to the study of second language learning. In the development of the methodology, applicable techniques from first language acquisition research were incorporated and new techniques appropriate specifically to second language acquisition were devised. The research examined the acquisition of English by six Spanish-speaking subjects over a ten-month period. Two subjects were at each of three target ages: 4-6, 11-14 and over 18. Each subject was visited approximately every two weeks and speech samples were recorded in three situations: spontaneous speech recordings, elicitations and pre-planned sociolinguistic interactions. The subjects were "free" second language learners with very little or no prior or current instruction in English. Thus they acquired their second language mainly by exposure to the English-speaking environment. The analysis focused on the acquisition of the English auxiliary and its related structures, the negative and interrogative. A clear developmental pattern was found for both the negative and interrogative. A highly variable order of acquisition was found for the appearance of auxiliaries. (Author)