but some people blame teachers should be responsible instead of politicians
Maybe you mean "but some people argue that teachers, not politicians, should be responsible"?
There is no doubt, the job of the teacher is to deliver good teaching
I feel like "there is no doubt that the job..." sounds smoother. Also, maybe replace the word "good" with something like "adequate" or "excellent". (try a thesaurus.)
They can also decide too much variation in the stands and qualification.
Sentence seems too short compared to the other sentences. Merge with previous one.
While Some people argue
You capitalized "some"? lol. Also in that sentence you should put a comma, not a period.
Instead of "But it is true" try "regardless"