Background: The first semester in undergraduate engineering is often challenging for students, making this a potentially fruitful time period for exploring motivational changes and relations between motivational beliefs and achievement. Purpose/Hypothesis: The purpose of the current study was to examine changes in implicit beliefs about intelligence and effort beliefs across the first semester of undergraduate engineering education, to investigate how these beliefs may contribute to first-semester achievement, and to explore changes in students' perceptions of the relative contributions of effort and ability/intelligence to grades. Design/Method: Data from first-time, full-time engineering undergraduates at a large Midwestern university were collected at Weeks 1 and 13 of the first semester. Analyses were replicated across two cohorts (2013 and 2014). Results: On average, students entered and ended the semester with relatively incremental and positive effort beliefs. Surprisingly, incremental beliefs did not predict grade point average (GPA). Positive effort beliefs were associated with GPA in both cohorts. Findings regarding the role that perceived effort plays in achievement were replicated across cohorts. The average trajectory was as follows: at Week 1, students perceived that ability/intelligence was the primary contributor to high school achievement but anticipated that effort would play a greater role in undergraduate coursework; at Week 13, students on average reflected that the role of effort was less than originally anticipated. Conclusion: Although implicit beliefs about intelligence and effort beliefs remained fairly stable across the first semester, students in both cohorts exhibited similar shifts in perceptions of the importance of effort (relative to ability/intelligence) for academic success.