Student or Learner
Is ''You are not teaching your students in an effective manner. They are not getting on in their studies. Please pay more attention to them.'' correct?
I would use "effectively" instead of "in an effective manner". I'm not sure what you mean by "They are not getting on in their studies". If you'd said "They are not getting on with their studies", I would assume you meant that the students simply aren't studying. Did you perhaps mean that they are not improving in the unspecified subject. Is the last sentence an additional suggestion or are you saying that the reason the teacher isn't teaching effectively is that he/she is not paying attention to the students?
The final full stop you used should not be there because it's not the end. The question mark is the end.