Based on the information provided, if academic rigor and challenge are the top priorities, I recommend Cranbrook Schools as the best choice among the listed options. Here's why:

Academic excellence: Cranbrook Schools is known for its rigorous academic program, consistently ranking among the top private schools in the United States. The school offers a wide range of challenging courses, including Advanced Placement (AP) and International Baccalaureate (IB) options, ensuring students are well-prepared for college and future academic pursuits.

Outstanding faculty: Cranbrook boasts a highly qualified and dedicated faculty, many of whom hold advanced degrees in their fields. The low student-to-teacher ratio allows for personalized attention and support, fostering a strong academic environment where students can thrive.

Comprehensive curriculum: In addition to core subjects, Cranbrook offers a diverse array of electives, allowing students to explore their interests and discover new passions. The school's emphasis on interdisciplinary learning encourages students to make connections across subjects and develop critical thinking skills.

Impressive facilities: Cranbrook's 319-acre campus features state-of-the-art facilities, including modern classrooms, science laboratories, art studios, and athletic complexes. These resources provide students with the tools and spaces necessary for academic growth and exploration.

Strong college placement: Graduates from Cranbrook Schools consistently gain admission to top colleges and universities worldwide, a testament to the school's academic strength and reputation.

While the other schools mentioned, such as Culver Academies, Western Reserve Academy, Lake Forest Academy, Kent School, and The Frederick Gunn School, are also excellent institutions, Cranbrook stands out for its exceptional academic program and reputation.

However, it's essential to consider other factors such as school culture, extracurricular offerings, and the student's individual needs and preferences. Visiting the schools, interacting with faculty and students, and assessing the overall fit for the student will help in making the best decision.

I tutored a student in honors math class from Cranbrook. My feeling was that even through the school has very decent SAT scores, their academic course might not that challenge at all. By the way Kent has good academic reputation, especially in STEM fields.

In my opinion, Cranbrook and Kent are both good at academic , but it still depends on the student's level.

Not sure about overall academic rigorousness, but it has been a consensus that Kent has been very competitive among its admitted students from Mainland China.