The program aimed to form a 9-member girl group from a pool of 41 female participants, training them in singing, dancing and other "subjects" over an 11-week time period.
Super Junior member Kim Hee-chul acted as the show's 'homeroom teacher' while veteran actor Lee Soon-jae was the principal of the school.
Meanwhile, Lee Hae-in surprises people by doing poorly after losing her voice and another contestant, Som Hye-in, struggles with the lyrics.
[7] They then started dance lessons with Park Jun-hee and Stephanie, where students must learn re-choreographed version of "Treasure" by Bruno Mars and "Deja Vu" by Beyonce with both songs' chorus looped on a cycle.
Fitness instructor Yoon Tae-shik who has trained celebrities also performed a physical endurance test focusing on the lower body, especially hips, gluteal muscles and thighs with the students.
Students go through a morning run where they must also sing the school anthem in order to boost their lung capacity, cardiovascular fitness and correct vocalization technique.
Kim Na-yeon was the worst student in the mid-way point of the broadcast, so she had to plead for votes at the end of the live update.
Yoo Ji-Na, on the other hand, was praised after noticing the problems with the details of the formation, despite being a poor individual dancer yesterday.
Tasha and Bin Ha-neul (Sky) are tasked to check the formation, and they picked the five students that struggled (Kim Ju-hyun, Snowbaby, Yoo Ji-na, Jo Se-rim, and Lee Si-an) to train all night.
While Lee Si-an and Park Ji-won kept splitting off on the right side (on screen) of the W, They managed to perform as a whole group in the final take.
Students start the first Debut Diagnostics Exam in a live dance and vocal performance in CJ E&M Building where they will be split into teams of 8, and they will cover a girl group song each.
The leaders are predetermined by the teachers based on performances thus far and contents of their diary, but the team members are picked by the preferences of the remaining students.
In Performance Classes, taught by Stephanie, they learn to be able to find the operating camera and focus their eyes and body towards it, and jostle to ward the foreground in order to gain more screen time.
During Advanced Vocal Group's Practice, Jang Jin-young fixed Kim Na-yeon's vocals, and realized the song suits her very well, and her voice can be very similar to Sea (Bada), which was the reasons for her to get the Killing Parts which was also the high notes that Bada covered in the original song, but Na-yeon is actually the type that write many notes to aid her memory.
After the performance, Heechul went over from the students' waiting room for Bada's reaction, and stated the song was not sung live often, and they did very well, and Advanced Vocal Group won the match-up in an upset.
It would also give Jang Jin-young and Bada their only victory since Intermediate and Beginner's Vocal classes were already abolished due to last eliminations.
Park Soo-myeong improved by 33.3 points between the Basic Strength Tests to midterm, so she gained an extra +3 card as she was in the winning team as well.
Notably, Park Ji-won wanted to work on her comedic sense, given the school has no proper classes for such type of idols.
As a Special Star Quality Exam (related but separate from the Debut Diagnostics Exam), the remaining students host a series of extracurricular live broadcasts of August 25 on KakaoTV, with the topics to be determined by online members, the winners are determined by viewership numbers, with the members in the programs get Rankings +1 Cards.
Lee Sae-rom and Song Hayoung's Yoga Class won and both got Ranking +1 cards that helped them get to the top 2 spots.
The day after the special exam, Stephanie shared her experiences of living with 13 other trainees at one point, and how her ankles were badly damaged due to overuse by dancing on high heels for long periods of time, and took 5 years to repair, which included her major back injuries in 2010.
The songlists are (mentors): Initially, there was no maximum limit of members per song, but the students with the highest Exam score last time gets first pick, which was Park So-myung, but as the 'draft' unfolds, Wee Woo, No No No and Step got the most students as they are both easy to sing and are good for changing concepts, so the groups have over-saturated.
The first group to perform was Wee Woo group, where they went to Pledis Entertainment's training room to get tips from Pristin, they corrected the true killing part of the song from the choreography point of view, then each member was assigned to Pristin's member for individual training, except for Park So-myeong, who had help from Yuha and Eunwoo as she was the worst dancer.
The Debut Diagnostics Exams occur inside CJ E&M Center Studio located in Sangam-dong, Mapo-gu, Seoul.
On Episode 8, members went to various girl group idols' agencies in Seoul, including GFriend (Source Music), Twice (JYP Entertainment), Pristin (Pledis Entertainment), Kara (DSP Media, as Heo Youngji remains with the company as a solo artist) as their 'internship' and exclusive training for the final exam.
The song "Cause You're Pretty" (예쁘니까) which was sung by the 41 contestants, was released digitally by Mnet on July 13, the same day as the show's premiere.
Following allegations of electoral fraud in Produce X 101 that resulted in a lawsuit, the Seoul Metropolitan Police Agency also included Idol School in their investigation.
[18] In an interview with MBC, a trainee alleged that, throughout their six-month training period, the contestants were only given clothes appropriate for the summer and had to wear them in cold weather.
[19] Lee Hae-in's father alleged through her fan site that CJ ENM suggested during her audition that she sign with their subsidiary agency to ensure that she would be able to debut after elimination, and she had done so out of fear of not being accepted into Idol School.
[20][21] It was also revealed that producer Kim Tae-eun had eliminated Lee Hae-in from the new girl group that was formed through the show, despite her being ranked first in viewer votes.