Saying BTC affects students' performance at school is the same thing as saying any other hobby would affect the students's performance. If someone is able to make a fortune with stock trading, then the student might also put a lot of time into learning more about the topic and its methods.
It is indeed affecting the study of the students in their school because bitcoin is really distracting the students from their study because the students are putting more attention and time to bitcoin since they are earning money rather than putting their majority of attention and time to their study. As one of my friend is student and really making money in bitcoin, i agree with him that it is better to put attention in bitcoin compare to studies because his school is not giving him money.