Ahh, I remember a similar situation before. I played around with my friends before an English exam and they then all failed...then I remembered they all suck at English and I felt really bad that I forgot about it and led them around to play. They probably wanted an excuse to not study as well so they didn't express any disinterest and I never realised it either. They probably thought that because even me, who is good at this subject, is playing around...they don't need to worry either. Oh how wrong they were.