Changes in U.S. textbooks indicate that U.S. first-grade students in the Common Core era were exposed to a wider variety of word problem types than students in previous generations were. We compared the performance of U.S. first graders in the Common Core era with that of previous generations in solving 11 types of additive word problems to investigate a decades-long debate--whether certain types of word problems are inherently more difficult than others or whether relative difficulty is influenced by exposure. We found that overall patterns of relative difficulty persist; however, U.S. first graders in the Common Core era outperformed their historical counterparts when solving the types of problems that rarely appeared in textbooks used in the 1980s.