Constructivist teaching has been taken as a fashionable teaching in educational sector, especially in science teaching, without considering carefully the prototype theory of constructivist teaching which is genuinelly based on constructivism, a particular epistemology, and its inherent dilemma and limits. This paper attempts to examine this theory of knowing and its implications in teaching objectively and critically. Upon the conclusions, it was proposed that constructivist teaching should be taken as a promising one rather than an almighty one, among alternative perspectives of teaching theory, and be used appropriately to take advantage of its strength and avoid its weakness. This is to say, it can be used wisely for emphasizing the learner as an active role and encouraging him/her to participate more enthusiastically; adapting curriculum and instruction to individual differences; adjusting the teacher as a facilitator, a supporter, and a manager role rather than as a lecturer; harmonizing the relationships in a class as a social system; and focusing on teaching and learning process.