Tape Goofs *spoilers*
When one kid drops a tape in a boombox that people were dancing around to: he presses the last button on the far right (that's usually pause) & the music that was playing (radio?) just cuts out. We don't see him switch the mode to "tape."
When the teacher plays a confiscated tape of the memo in a cassette clock radio: the principal tells him to turn off it (so she can announce that Malcolm killed himself). He makes a gesture to the machine & the music cuts out. But we can still see the "play" button engaged & the tape running.