Are you obliged to give assessments? If not, don't even think about it. Given that you can, in ideal circumstances, devote less than one minute a week to each student as an individual, then you cannot realistically know anything significant about any but the outstandingly good and the outstandingly weak students.
If you are obliged to monitor progress and give assessments, be as positive as you can, even if you don't recall which student you are writing about. Whatever you write, be prepared for parents to ask you "Is my son/daughter the best in the class?" The safest answer is "Yes", preferably not in the hearing of the parents of other students - to whom you are going to say exactly the same thing.
I am sorry if this seems cynical/unhelpful, but this is what I learnt when I taught in China fifteen years ago. Things may have changed since then, but I doubt it.

English Teacher