Some bad ideas never seem to die, despite research showing they do not actually work. It can be hard to spot them at first. Those dispelled education theories that research shot down long ago. They creep up in studies, shuffling around mumbling in the reference lists, or moan loudly in blog posts. The author often stumbles across these "zombie ideas," despite researchers' best efforts to put them six feet under. In this article, the author takes a look at some of these (un)dead ideas and why educators need to stop giving them authority: (1) (Un)Dead Idea #1: Students Have Different Learning Styles; (2) (Un)Dead Idea #2: Students Learn Best Through Unguided Discovery; (3) (Un)Dead Idea #3: Students Should Learn to Read Through Authentic Reading; (4) (Un)Dead Idea #4: Students Don't Need Facts, Just Critical Thinking Skills; (5) (Un)Dead Idea #5: If It's Worth Teaching, It's Worth Grading; and (6) (Un)Dead Idea #6: Smaller Classes Are Better.