This year there are less students in the school.
This year there are fewer students in the school.
Use less + uncountable noun: ‘less time’, ‘less money’, ‘less food’.
Use fewer + plural countable noun: ‘fewer students’, ‘fewer mistakes’, ‘fewer cars’.
It is common to hear less before plural countable nouns in informal English, but use fewer in careful writing.
Check our grammar lesson on the difference between less and fewer.