Barrio Boy is a true story of the author's cultural transition from a small Mexican village to a barrio in the United States. Ernie Galarza's story is constructed from memory, beginning when he is about four years old and ending just before he begins high school. His detailed perceptions of the world around him paint an insightful picture of how socio-political factors and cultural experience can shape one's life and future.

In the first section of the book, Ernie describes village life in Jalcocotbn in detail. He talks of the daily routine, from how to cook tamales to how to interact with adults. In doing so, he builds a context with which to compare the experiences that follow. Those experiences come as a direct result of the escalating revolution between the Mexican government and its working class. To Ernie, the fighting occurs in the background and he learns of the danger to his family only by eavesdropping on adult conversations. While he doesn't completely understand the factors behind the revolution, he is forced to deal with the consequences. The primary consequence is that he and his family must give up their farming lifestyle and learn to support themselves by working for pay.

The journey of the Galarza family takes them from Jalcocotbn, Tepic, Acaponeta, Casa Redonda, Mazatlbn, Nogales, and Tucson before they finally land in Sacramento, California. The early legs of these travels show that cultural transitions occur not only between countries, but also between cities and villages within a single country. The lifestyle Ernie and his family adopt in Tepic is much different from that they experience in Jalcocotbn. In each new environment, the Galarzas have to adjust to new ways of doing things, as emphasized by Ernie's descriptions of daily activities such as shopping and working. These experiences foreshadow the ultimate cultural transition that awaits the Galarzas, learning to live in America without losing touch with their Mexican heritage.

The Galarzas leave the revolution behind once and for all when they cross the border into the United States. Unfortunately, life in America offers its own sets of problems. They all must learn what it is to be culturally out of place in a country that does not understand them.

Ernie describes the diverse sights and sounds of the barrio as a reporter would, documenting the people and places that stand out in his memory. In total, these experiences shape Ernie's mindset about his own future and stimulate his desire to make something of himself. At the close of the book, Ernie has become an educated young man who understands work ethic, familial responsibility, and every man's right to be treated with dignity.