mark (someone) down

Translations
понижать оценку
The teacher decided to mark him down for his incomplete assignment.
Учитель решил понизить ему оценку за незавершённое задание.
Definitions
To reduce the grade, score, or evaluation of someone, often due to mistakes, errors, or not meeting certain standards.
Words
mark

verb
снижать оценку
someone

pronoun
кого-либо
down

adverb
вниз