- The teacher seemed to be very easy to teach the students.
- It was easy to teach the students.
(1) First, notice that I got rid of "seem." "Seem" is used to introduce uncertainty, and if the speaker is confident that teaching the students was easy, then it's usually unnecessary. If you think "seem" is necessary, then get rid of "to be":
- It seemed easy to teach the students.
(3) I got rid of "teacher" because it's implied. Who teaches students? A teacher! If it's implied, then it's unnecessary.
(4) The impersonal subject "it" refers to the situation, in this case, the classroom situation. The British Council has a good explanation of when we use the impersonal, or "dummy" subjects "it" and "there." I recommend that you read this carefully because this causes many problems.
In summary: simplify your verb, avoid over-emphasis and implied ideas, and learn to use "it" and "there" correctly.
Please use English well!