Correct harshly, on a harsh way, strictly ??? And what's the opposite?
How should I express it
It's better to correct harshly than lenient ???
So students get to the exam day with a high level ???

Thank you

Question

Correct harshly, on a harsh way, strictly ??? And what's the opposite?
How should I express it 
It's better to correct harshly than lenient ???
So students get to the exam day with a high level ???

Thank you

Answer

"It's better to be strict than lenient with corrections." or "It's better to correct strictly than leniently."
Being harsh means that you are too strict, and perhaps unfair in your evaluation.

Non perdere l'opportunità di imparare una lingua comodamente da casa tua. Esplora la nostra selezione di insegnanti di lingue esperti e iscriviti subito alla tua prima lezione!