This study is intended to help experienced practitioners and student teachers gain a systematic understanding of language learning. Part I is a general introduction discussing the second language learner and first language learner. Part II describes the adult interview study; the method, procedure, and results of interviews with good and poor language learners are outlined. Part III describes the main classroom study, which constitutes the major portion of the report. The following aspects of the study are discussed in detail: (1) apparatus (criterion measures, cognitive style and personality test, classroom observation and student interview); (2) method; (3) results and statistical analysis; and (4) special aspects (such as differential teacher treatment, case studies and classroom activities and atmosphere). The study involved a total of 72 students in grades 8, 10 and 12, who were observed and then tested in an attempt to isolate some of the critical variables among the common characteristics, personality traits, cognitive styles, strategies and learning environments of the good language learner. Part IV, the conclusion, discusses major findings, suggestions for further research, and practical implications. Rubin's list of strategies, the interview questionnaire, and a bibliography are appended. (NCR)