April Kepner failed her board certification in 2012, but re-took her certification in 2013 and passed. According to the @GreysMedical twitter, Jackson Avery is double-board certified in plastics and ENT like Mark, later confirmed in show's dialogue.

What episode does April Pass boards?

Let the Bad Times Roll.

Why did April fail her boards?

In the end of season eight, Kepner embarks on a relationship with her best friend turned lover Jackson Avery (Williams), who she loses her virginity to and that eventually leads her to reflect on her faith and fail her boards.