Ambiguity tolerance reflects learners’ abilities to accept unpredictable and unfamiliar contexts in language learning without frustration and discomfort. However, it has yet to be thoroughly explored when associated with engagement, motivation, and peer collaboration collaborative learning in course of English as a foreign language (EFL) learning. Relying on questionnaire survey data, this study adopts structural equation modeling techniques based on 1,200 Chinese high school students’ responses. The findings ascertain that engagement and volition significantly and positively predict ambiguity tolerance and learning effectiveness. Additionally, ambiguity tolerance predicts learning effectiveness. For peer collaborative learning, ambiguity tolerance and learning effectiveness are also critical predictors. They significantly and positively predict collaborative learning willingness. Moreover, ambiguity tolerance predicts peer feedback acceptance but not sensitivity to peer pressure. Learning effectiveness significantly and negatively predicts sensitivity to peer pressure, but its impact on peer feedback acceptance is insignificant. Dominant strategies for high school English learners to cope with unfamiliar and uncertain contexts are external help-seeking from dictionaries and instructors. The findings in this study contribute to educational research on psychological mechanisms behind ambiguity tolerance, language education in high school, learning effectiveness, and collaborative learning. As such, this study encourages continued efforts to explore such topics and the consideration of ambiguity tolerance in teaching practice.