Semi-fixed templates with open slots such as bu-A-bu-B (not-A-not-B), qian-A-wan-B (hundred-A-thousand-B), A-yan-B-yu (A-words-B-utterances) abound in Chinese idioms and are used productively in discourse (Ching 1964; Zhang 2002; Ji 2007). Yet the productivity of these schematic idioms is not unrestrictive since possible A, B morphemes that fill in the open slots must conform to certain structural and semantic constraints. How children come to learn the constraints on their productivity raises an interesting issue in language acquisition. This pilot study investigates young and adult native speakers’ competence on the partial productivity of Chinese schematic idioms in terms of three related constructions -- XAXB, XAYB and AXBY (in which X and Y are the fixed templates), and explores the factors that influence their acceptability judgments. Specifically, this study tested the effect of input frequency, structural complexity, internal semantic relation and chunk effect of open morphemes with 4th graders and adults in a graded Grammaticality Judgment task. Results showed even 4th graders began to form abstract generalizations on the legitimate words that can enter the open slots of schematic expressions. The results provided empirical support for the psychological reality of constructional claims for idiomatic expressions under Chinese context.