PHILADELPHIA — Like many of his third-grade classmates, Mario Cortez-Pacheco likes reading the “Magic Tree House” series, about a brother and a sister who take adventurous trips back in time. He also loves the popular “Diary of a Wimpy Kid” graphic novels.

But Mario, 8, has noticed something about these and many of the other books he encounters in his classroom at Bayard Taylor Elementary here: most of the main characters are white. “I see a lot of people that don’t have a lot of color,” he said.

Hispanic students now make up nearly a quarter of the nation’s public school enrollment, according to an analysis of census data by the Pew Hispanic Center, and are the fastest-growing segment of the school population. Yet nonwhite Latino children seldom see themselves in books written for young readers. (Dora the Explorer, who began as a cartoon character, is an outlier.)

Education experts and teachers who work with large Latino populations say that the lack of familiar images could be an obstacle as young readers work to build stamina and deepen their understanding of story elements like character motivation.