Student or Learner
If your academic performance was neither too good nor too bad, just around average level, how do you say that?
For example, your ranking was like 15~25th among all the 40 students in your class.
I was an ordinary student?
I studied so so?
I am not a teacher.
'I was an average student' is probably the best fit.
'Mediocre' and 'so so' work too, but they have a connotation of slightly worse than average.