I'll give an example of elementary teachers teaching math
They teach 1 to 10 instead of 0 to 9
Our number system is base 10

Most don't even know that.

I had one teacher say that teaching 0 would be confusing to the kids.  What kid doesn't understand the value of nothing.  
Have one apple and take it away - o (zero apples).

Finally, everyone learns differently, yet every time the curriculum changes, so does the teaching method.  Education bureaucrats want to pigeon hole each kid into a learning method based on what's worked for them and suggest that just by changing it, problem solved.