There are many reason if your essay fail to get the grade you want, here we have the list of grading standards your teacher mark your essay:

Excellent (A or over 70)

A consistently authoritative grasp of the concepts, methodology and content appropriate to the subject area, demonstrated through depth and confidence in understanding of issues underpinning the assessment task.

Very good (B or 60-69)

A confident level of understanding at this Level, based on an assured grasp of relevant concepts, methodology and content, demonstrated through evidence of significant skill in interpreting complex material articulated with a high level of competence.

Good (C or 50-59)

A coherent response at this Level to the requirements of the assessment tasks, demonstrated through evidence of accurate restatement and organisation of relevant concepts and material.

Acceptable (D or 40-49)

A response that shows awareness of the requirements of the assessment tasks demonstrated through evidence of some reading and organisation of relevant source material and of an attempt to draw relevant conclusions. Evidence of attainment of all learning outcomes described at threshold level.

Unsatisfactory (E or 30-39)

Work that does not show achievement of some learning outcomes at threshold level, but which may demonstrate sufficient evidence that a D grade is not wholly beyond the grasp of the student.

Unacceptable (F or blow 30)

Work that does not demonstrate the achievement of learning outcomes at threshold level.