I got a few correct solutions to the puzzle – Suman Saraf, Manjiri and Karan Sharma. Congratulations to all three!
Answer: Boys count out at interval of 14 and girls count out at interval of 13. Unfortunately, I was hoping that there would be a trick to it, but could not find any specific trick. That said, it is easy to eliminate possibilities quickly counting from the bottom.
Hope you all enjoyed the puzzle.