The situations people find themselves in and how they experience them is fundamental to a host of life and work outcomes. However, most research has so far only relied on self-reports and is thus not able to disentangle different situation components. The present study therefore examined the dynamics between self- and other-rated situation characteristics, personality traits, and personality states in an educational setting. One hundred and seventy-three student teachers (n = 2,244–2,261 observations) and 94 supervisors (n = 1,110–1,122 observations) participated in a 13- or 14-day experience sampling study during student teachers’ internships and rated situations and teachers’ personality states twice daily. Answering three research questions yielded that 1) self-rated traits were mostly not associated with self- or supervisor-rated situation characteristics; 2) self- and supervisor-rated situation characteristics predicted self- and supervisor-rated personality state expressions (although effects were largest for same-rater associations); and 3) there were no interaction effects of traits and situation characteristics on personality state expressions. These results have important theoretical and applied implications as they advance our understanding of person-situation dynamics in an applied setting and suggest that associations between situations and personality states are not solely attributable to common rater effects.