This study examined the relationship between the open-endedness of activities and the creativity of young children. Eleven prekindergarten classes were observed and rated twice using a researcher-developed instrument, the Open-endedness of Activities Rating Scale (OARS). Three classes were selected from the 11 based on their cumulative ratings in the first observation (CROBS1): the class with the lowest degree of open-endedness of activities (CLSL), the class with a medium degree of openendedness of activities (CLSM), and the class with the highest degree of open-endedness of activities (CLSH). Fifty-two "atrisk" students in these three classes (24 boys, 28 girls), who had no identified disabilities or delays, were tested utilizing Torrance's (1981) Thinking Creatively in Action and Movement (TCAM). A correlation was then drawn between the three classes' ranks of CROBS1 and their respective ranks of mean TCAM scores: fluency scores (FLUE), originality scores (ORIG), imagination scores (IMAG), and total scores (TTCAM). The 11 classes' CROBS1 was correlated and compared with their cumulative ratings in the second observation CROBS2 in order to examine the reliability of the OARS. The results from the study indicated that: (1) the researcher-developed instrument, the OARS, is reliable for research purposes; (2) the degree of openendedness of activities is significantly positively related to the level of creative thinking ability of the young children engaged in these activities; (3) increasing the open-endedness of activities is most beneficial for a class with a relatively low degree of openendedness, because a moderate increase in its open-endedness can result in a noticeable improvement in the fluency, originality, and total creative thinking ability of its students; and (4) increasing the open-endedness of activities is also beneficial for a class with a relatively medium degree of open-endedness, because a moderate increase in its open-endedness can result in a noticeable improvement in its students' imagination.