Cora the mermaid has recently entered third grade, and is finding learning to spell challenging. Her mother gives her an enchanted tortoise-shell diary and some octopus ink, and encourages her to write up her experiences. It will help her improve her spelling, and give her a place to work out her emotions. Cora is more interested in swimming: she has made the junior swim team, known as the "Singing Sirens," but the coach informs her that unless she improves her bad grade in spelling (a "Fish without the –ish"), she is off the team and her spot and her swimming cap will be taken by her arch-nemesis, Vivian Shimmermore, whose skin is so beautiful it glows. Cora’s friends, Sandy the mermaid, Jimmy the jellyfish, and Larry the sea-cucumber, advise her that all she has to do is study, but Cora is not convinced. She goes out exploring in the sea, and reaches the dumping zone, where humans dump their rubbish. There, she sees a shrimp, caught under a barrel of sludge. Cora pushes the barrel off the shrimp, and goes home. But the shrimp, doused in a drip of sludge, grows to a huge size, and follows her home, where it plays games with Cora. In the morning, Cora’s little brother has a swollen face – he is allergic to shrimp – and needs to see the doctor (Dr Beluga). Assuring her mother that she has not got a "little" shrimp in her bedroom (rather than a whale-sized one), Cora stays behind to study her spelling homework. But the shrimp, whom Cora has named "Salty," wants to play fetch. Cora tricks a tuna into carrying away the stick, and Salty swims far away after it. Alone in the sea without Salty, Cora is suddenly surrounded by sharks, including Magilla, the "not-so-great-white-shark," who teases Cora. When she teases him back, Magilla chases her, along with his friends. She hides in a shipwreck, posing as a figure-head, but is surrounded. Luckily help arrives, in the form of Salty the Shrimp. Cora and Salty play until both fall asleep. Rather than being annoyed when she sees Salty, Cora’s mother, returning from the doctor, is proud that Cora has saved a creature in need. 

Next day, Cora is out for a swim when she bumps into her rival, Vivian Shimmermore. Vivian is exquisitely pretty, the youngest of the famous Shimmermore sisters, whose siren song lures sailors to destruction. Cora is jealous of her beauty, but wonders why she has never heard Vivian sing. Vivian’s older sisters, Belinda and Arabella, demonstrate their singing, luring a boatload of sailors who are entranced by their beautiful voices, but suddenly Salty leaps out of the water, breaking the mood. Nevertheless, the Shimmermore sisters invite Cora to their birthday party, to the ire of her friends (Sandy, Jimmy and Larry). The next day, on a school field trip to the kelp forests, Cora discovers Vivian eating kelp to enhance her skin with clorophyll, and confronts her, accusing her of eating the forests they were supposed to be protecting, in order to fake a beautiful glow. Vivian disinvites Cora from her birthday party. But Cora shows up anyway, with the support of her friends (who have been reading her diary and know where she’s going). She reveals the secret of Vivian’s glow, but it turns out that all the Sirens eat the clorophyll. Suddenly, the birthday lava-cake explodes – it is located on top of an underwater volcano, and Vivian’s birthday party has to flee. Cora goes home and studies for her test. Back at school, Cora takes her spelling test, getting an A+. (The words on her list are words from her experiences during the previous days, reinforcing them for young readers.) She tells the coach, however, that she does not want to be in the Sirens after all, and goes home to spend time with her proud mother, who informs her that the diary was not enchanted at all, that she was writing under her own inspiration. 

Third Grade Mermaid is a chapter-book for 8–10 year old readers that uses a diary format to tell Cora’s story. For the most part, it is a story of school rivalry, set in an underwater world to add interest. Cora, the mermaid, overcomes a range of challenges: working on her spelling, dealing with unfairness, rivalry, bullying and friendship, learning to care for others, and to care for the ocean. The themes that run through the story incorporate schoolyard politics with a sense of ecological consciousness. The list of words that Cora has to learn to gain her A+ are ecological in nature ("drifted, toxic, species, predator, exoskeleton, ecosystem"), and her adventures underwater involve ideas about caring for nature, cleaning up the ocean, and protecting vulnerable species, suggesting an underlying didactic purpose. 

Classical elements of the mermaid myth are interwoven throughout Cora’s story, largely focusing on the idea of the singing sirens, whose song lures unwary sailors into peril. The Shimmermore sisters are beautiful and blessed with lovely voices, as per the myths. Cora’s jealousy of Vivian’s prettiness is cast as a traditional school rivalry, with Vivian functioning as the traditional high school "mean girl." 

The text is accompanied by lively cartoon images, which break up the flow of words, and allow young readers to visualise the story. Cora’s frequent misspellings (always crossed out and corrected) may resonate for children who are learning to spell, and encourage them to develop skills in literacy: at the end of the novel, Cora’s mother notes that despite her spelling issues, Cora loves to write, and to express herself. In many ways, Third Grade Mermaid travels a long way away from the sirens of the Odyssey, but its connections to creativity, beauty, and art, are nevertheless traditional. Despite its (somewhat belated) emphasis on individual creativity, the story does not interrogate a focus on beauty and "popularity." 

"Peter Raymundo, Peter Raymundo: THIRD GRADE MERMAID", Kirkus Reviews, October 15, 2016.

Persohn, Lindsay, "Raymundo, Peter. Third Grade Mermaid", School Library Journal 62.11(2016): 84.

"Raymundo, Peter" in Something About the Author, vol. 324, Jennifer Stock, ed., Farmington Hills, Michigan: Gale, 2018, 147–148.

Third Grade Mermaid at amazon.com (accessed: September 16, 2020).