Ably demonstrates finding thoughtful solutions for common problems.Cole's educational story brims with math problems that characters solve (readers can also find the solutions). The bright, young cast is likable despite Stephanie and Justin's squabble (both sides have reason to be hurt). And it's a delight when Catherine and Jordan work hard to fix real-world problems. While this installment is less exciting than others (which involve burglary, kidnapping, etc.), it shows how everyday life can sometimes hit the hardest. O'Toole's black-and-white artwork leaves lasting impressions, whether filled with detail (Justin's packed but organized room) or deceptively simple (the Math Kids' hands raised in unison). A helpful appendix clarifies some of the more complex mathematics, like the order of operations.

– Kirkus Reviews

A Knotty Problem features all of the scintillating brain-twisters that one associates with the series, while its more personal stakes have a grounding effect. The Kids' abilities may be extraordinary, but the challenges they face are much the same as those that average fifth-graders face, whether over maintaining the bonds of friendship in difficult times, or learning the value of teamwork on a soccer field or during a high-pressure quiz.As always, the book supplies plenty of useful math knowledge, ranging from the concept of the Gordian Knot, which plays a key role in the resolution of Justin's dilemma, to a biography of George Polya, the “father of problem-solving.”And its characterizations are deft, so that the Kids' squabbles and efforts to do what's right are heartwarming.Charming illustrations complement the book's friendly tone.Capped off with a tense final math showdown (the full solutions for which are included in the book's informative appendix), A Knotty Problem continues the Math Kids series' streak of providing entertainment and enlightenment.

– Ho Lin, Forward Reviews

"Libraries seeing popularity with the prior Math Kids adventures, as well as newcomers looking for vivid fictional stories embedded with math problem-solving concepts, will find The Math Kids: A Knotty Problem a fine tale that educates as it entertains."

– DIANE DONOVAN, Midwest Book Review

The four protagonists are realistic and relatable. As well as modeling problem-solving in real-life situations for readers, they reinforce a key message throughout the series: Math is not just for geeks and not just for school. A Knotty Problem focuses on an idea that many kids—and especially intelligent ones—find challenging: the idea that not every problem has an ideal solution.Shannon O'Toole's old-school black and white illustrations keep this chapter book accessible, while an appendix at the end explains the Math concepts for readers who want to learn more.Overall, A Knotty Problem is instructive and enjoyable, offering readers a thought-provoking story about how STEM can help with everyday problems and situations.

– Dr. Jen Harrison, The Children's Book Review

"Libraries seeing popularity with the prior Math Kids adventures, as well as newcomers looking for vivid fictional stories embedded with math problem-solving concepts, will find The Math Kids: A Knotty Problem a fine tale that educates as it entertains." Midwest Book Review

– Midwest Book Review