SNSD's Yoona made an attempt to dress up as a guy. She transformed into a boy in black suit in SBS's Family Outing Season 2 (FO2).

The episode took place at Jun-nam Kwang-yang Sum-Jin Village, with a request to advertise the 'Plum Festival'. 'Mr. & Ms. Plum Contest' was held, female members becoming Mr. Plum, while male members became Ms. Plum to show off their individual talents.

Yoona performed Shinhwa's 'Wild Eyes' by transforming from a cute and pretty girl into a handsome boy. She reenacted the chair dance perfectly and made everyone laugh by saying that she was 'a guy looking for employment who hasn't even gone to military yet'.

Handsome boy Yoona and the best 'Mr. & Ms. Plum' chosen by village representatives will be revealed on March 21 on FO2.

don't like the new FO but i love this dork~♥
soshified.

As idols debut sooner and sooner, there in an increase in the interchange between their school life and celebrity activities. 
After stars born from the 90’s began emerging, there were many cases where these idols attended college or high school while simultaneously filming television broadcasts but now it is not uncommon for trainees in elementary school to debut during their junior high school years. This can be seen with recently pointed out stars such as Kara’s Kang Jiyoung, f(x)’s Sulli, Krystal, and 4minute’s Kwon Sohyun to create the “girl group ‘94 line.”

Managers who are in charge of these idol singers with middle school and high school identities tend to visit the idol’s teacher rather than the singer’s parents or the singer themselves. This is due to the fact that a student can graduate only if they fulfill certain attendance requirements. Although this differs from school to school, because the number of attendance required must be fulfilled, young idols tend to use various methods to fulfill requirements such as coming to class partially for the day.
T-ara’s Jiyeon is in her second year of high school where she told a reporter, “At school, I want to meet friends and study. But when you start planning out the schedule, it becomes difficult since there’s simply not much time left.”

New high schooler U-Kiss’ Dongho also revealed, “I rarely have time to go to school. Next Monday, it was decided I would attend school. I’m already excited.”

In order to appear on a music program, you need to start preparing your hair, makeup and other things early on in the morning so the day becomes short. These music programs are centered on airing during weekends so technically you can say that weekdays are more of the “free days” for singers. However, during these “free days,” stars have to appear on radio programs, film, or prepare for their next stage so even if they make time to attend school, they often just end up showing their face.

Source: allkpop