Forbidden Topics

Are there any topics that shouldn't be taught in school? 

I believe that there are certain topics that should not be taught in school, but not to the point of censoring everything. There is certain age levels that people should learn such subjects and that's what teachers do in each grade. They explain topics with more maturity required in higher grade levels and less explicit topics in lower grades. I think that teachers do a good job at teaching us everything, from controversial subjects to the smallest little subjects, I think that exposing students to controversial subjects gives them a better understanding in case they are presented with the subject later in life. Students and people not exposed to the subject will not be prepared to encounter them if they encounter it anytime in their lives.