The prism of grammar takes a closer look at what children's earliest language reveals about their thinking processes while also revealing something about their nuanced personalities. Attempting to close the distance between language development research and the children at the root of it, Tom Roeper invites readers to discover their own evidence for the book's claims through interspersed experiments. This interactivity proves that young children do not simply name objects, but also simultaneously reveal how they see the world and their relationship to it. Roeper's analysis clearly captures the sheer challenge confronting young children in becoming competent and proficient speakers of their language.

In Part 1, “Goals and grand perspectives,” Roeper lays out his objectives and his perspectives on language development. This includes his approach of using errors in children's language to better understand what they do know about grammar. Roeper believes that grammar has the tremendous power of conveying motivations. Recognizing this not only alters how kids are treated, but models humanism for children to adopt. In Part 2, “Why language acquisition is a challenge to the child,” Roeper elaborates on the why behind the what that kids provide (33). Through the close examination of key linguistic skills, such as the use of articles, negation, and quantifiers, Roeper highlights the development of thought and the creativity inherent in language production. He challenges readings of children's early language as egocentric, which can undermine the importance of social relationships not only in language development but also demonstrated linguistically through a child's concern and sympathy. Roeper cautions against “assuming a simple connection between grammar and cognition” but importantly, warns against ethical repercussions that do not respect the dignity of the child, such as a “label of inferiority,” which can unconsciously impact actions and relations with that child (193). Part 3, “Microdialects and language diversity,” is Roeper's examination of linguistic diversity. Language reflects identity as well as helps make judgments about others; this may lead to discrimination, which can be reinforced through an education that prizes certain ways of talking over others. Roeper points out that language prejudice is powerful, yet largely overlooked. As language indexes key information about the speaker, Roeper argues that differences between languages (in grammar or ways of speaking) can, without care, instill space for prejudice and discrimination. Instead, respecting diverse languages teaches underlying positive ethics.

In Part 4, “Finding philosophy and morality in every sentence,” Roeper look at the ethics behind children's language. Not only does this reveal the importance of avoiding the assumptions about what a child does not know, it is also about dignifying the thoughts and feelings of the child that may be at the heart of speech. Rather than speculate about why a child is behaving in a certain way and oversimplifying the behavior by attributing it to a child's egocentrism, Roeper advocates for recognition and respect for the dignity of children, their understanding of social relationships, and for what they are able to grasp. In this way, adults model and reinforce positive ethics. Across Roeper's book, he demonstrates and engages the reader in discovering that delving deeper into a child's early language shows tremendous awareness that children reveal from their first words.