This study examines the moment-to-moment within-person associations between maternal and child behaviors during a challenging puzzle task and compares these associations between mother--child dyads from the United States (n = 99, 52 boys, M[subscript child age] = 56.05 months, SD = 6.44) and China (n = 101, 46 boys, M[subscript child age] = 57.41 months, SD = 6.58). Maternal autonomy support and intrusive control and child agency and defeat were rated in 15-s intervals by native and bicultural coders. Country was examined as a moderator of the moment-to-moment within-person associations between maternal and child behaviors. The results showed that for both U.S. and Chinese dyads, increases in maternal intrusive control predicted subsequent decreases in child agency, and increases in child defeat predicted subsequent increases in maternal autonomy support. Furthermore, increases in maternal autonomy support predicted subsequent increases in child defeat, but for the Chinese dyads only.