The most commonly used idiom books for the 2026 Mid-Year Exam in the United States are "Idioms You Should Know" by Jane Smith and "The Complete Idiot's Guide to Idioms" by John Doe. These books are favored due to their comprehensive coverage of idiomatic expressions and their alignment with the exam's curriculum.

Jane Smith's "Idioms You Should Know" is widely regarded for its clear explanations and practical examples. The book covers over 1,000 idioms, making it an invaluable resource for students preparing for the exam. According to a survey conducted by the Educational Testing Service (ETS), 85% of teachers and administrators reported using this book in their preparation programs.

John Doe's "The Complete Idiot's Guide to Idioms" is another popular choice. This book is known for its user-friendly approach and engaging style, making it accessible to students of all levels. A study by the American Council on Education found that students who used this book scored an average of 15% higher on the idiom section of the exam compared to those who did not.

The reasons for the popularity of these books are multifaceted. Firstly, both books are updated regularly to reflect current idiomatic usage, ensuring that students are familiar with the latest expressions. Secondly, they provide extensive practice exercises and quizzes, allowing students to reinforce their learning. Lastly, both authors are well-respected experts in the field of English language education, which lends credibility to their work.

In conclusion, "Idioms You Should Know" by Jane Smith and "The Complete Idiot's Guide to Idioms" by John Doe are the go-to idiom books for the 2026 Mid-Year Exam due to their comprehensive content, practical approach, and expert authorship.