The New English Teacher

The New English Teacher

David was is [it is better to use present tense here because if you used past tense, it means that he is no longer a teacher or teaching English anymore.  It can also mean that he is no longer living etc.]an English teacher who just had [correct use of past tense since the act is of the past] graduated from the University.

Although he was is [same reason as above] very good at English it, [understood because of your first paragraph] and especially in grammar., However, he was not lacks humor [or you can also say, "he is dour/drab/humourless"] So his students felt feels his English class was is very dull and boring.

In his English class, some students wandered their eyes aimlessly looked around; some students whispered in conspirational tones [just to make your writing more interesting] and even some students rested on put their heads on the table desk to sleeping.

David felt that what he is doing he is very serious.   in the performance of teaching, However his students learnt nothing - they cannot pronounce even the simplest word properly.  ， even the simplest pronunciation. He was so very worried and annoyed. but There was nothing he can to do but to stared at these his students with in anger.

The New English Teacher

The New English Teacher
David is an English teacher He just had graduated from university when he became our new teacher. Although he was very good at English, and especially at grammar, he was not very humorous. So his students found his English class very boring.
Students would often look about during class, and sometimes whisper to each other. Some of them would even put their heads on the table on fall asleep.

David was very serious when teaching. Nevertheless, his students learnt nothing， not even the simplest pronunciation. He would get worried and annoyed, and he couldn't help but stare at his students angrily.