The worst things a teacher can do are mostly concerning their relationship with their students. Since this is the vital ingredient to teaching, anything which lessens or destroys that relationship is the “worst” thing that a teacher can do. Note that these are certainly not in order of which is worse than the other. All can have equally negative impacts on the teacher’s ability to effectively communicate their lessons.
Talking down to students is a primary, but often-ignored, fallacy of teachers. Teachers know more about many things than the students do, but taking that knowledge superiority and assuming that makes them better than the students puts teachers in a position it is easy to condescend from. This is particularly oft-occurring in relation to those students who know the least, and are therefore the most in need of learning. Teachers rarely talk down to high-performing students, but conversely these are also the students least in need of their help.
Among other factors, the above can lead to student favoritism, an even more common problem, and one potentially even more dangerous. Teachers tend to treat high-performing, well-prepared students much better than they do those students who seem less interested or less talented. This ignores the primary factors that contribute to performance and preparedness, which have nothing to do with intelligence or potential, and everything to do with poverty, negligence, and lack of opportunity. Those students who have struggled most with their development have their own lack of self-esteem reinforced by teachers treating other students more favorably. This can serve to handicap these students, potentially throughout their lives.
One significant problem a teacher can have that does not have to do with students is their interaction with their bosses and peers. Because of the relative isolation of the teaching profession, it is easy to become insular in practice, never seeking assistance or asking for clarification of policies or expectations. Many teachers assume they are on their own and that hard work will spell great results. This is particularly bad for new teachers who fail to take advantage of the expertise of their peers. Potentially even worse are violations of policy or lack of compliance with school district guidelines which can torpedo a promising teacher’s career rapidly.
The extreme examples of teacher misbehavior, such as physical violence, verbal assaults, and sexual interaction have been purposefully ignored here, because those teachers who are so massively misguided as to engage in these activities should be considered criminals, not teachers who would take advice to improve their technique. These are indeed the “worst” things a teacher can do, but only the most immature and ill-placed teachers would even consider them.
The worst things a real teacher can do is treat their students as anything other than the potential leaders, scientists, teachers, and guardians of all of our tomorrows.