The aim of the present study was to examine the intraindividual level and instability of perceived academic control (PC) among first-year college students, and their predictive effects on academic achievement. Two studies were conducted measuring situational (state) PC on different schedules: Study 1 (N = 242) five times over a 6-month period and Study 2 (N = 80) daily over a 2-week period. Consistent across both studies were confirmatory factor analyses and structural equation models demonstrating significant PC instability, as well as negative correlations between intraindividual PC levels (average across measurements) and instability (standard deviation across measurements). Also, in both studies PC level positively predicted subsequent academic achievement, although no significant PC instability first-order effects were found. Both studies revealed a PC level by instability interaction, as students with high-unstable PC typically received poorer grades than high-stable PC students. Study findings highlight the importance of considering both PC level and instability, and identify a previously unknown group of first-year college students at-risk of under-achieving academically--students with high-unstable perceived control. (Contains 3 tables and 2 figures.)