This study investigates the development of metalinguistic skills, particularly ambiguity detection, and whether training accelerates this development for prereaders in kindergarten (5;5-6;6). It is the first to compare homophone detection with lexically ambiguous sentence detection in which the same homophones appear. The experimental group received ambiguity detection training; the control group received vocabulary training. Results showed that there is a spontaneous development of homophone detection abilities at the end of kindergarten, and training may accelerate this trajectory. The development of lexical ambiguity detection is not apparent in kindergarteners. However, explicit training improves this trajectory significantly. The knowledge of both meanings of a homophone is not sufficient to report both meanings of a sentence that contains that homophone. We propose that detecting the dual meanings of an ambiguous sentence involves sentence processing operations and an ability to think flexibly about language that may be enhanced with training.