あんな風に勉強せずサボってたら成績は下がるわなの英語

You'll need to work much harder if you are going to pass the exam.

If you keep cutting classes, your grades will suffer.

Work hard, or you will fail―get plucked.

No wonder [Small wonder that] he passed the entrance examination; he works so hard.

I cannot have my grades fall, so I studies hard.

Work harder, or―else―or else―otherwise―you will fail.

You cannot make a good mark without working hard.

You could also say that he's at the bottom of the class, for sure.

Don't give up; you'll get there in the end if you keep studying.

He ought to have succeeded―should have succeeded―after his labours. （It is strange that he should not have succeeded after all his labours）

If you don't get down to work and study, you will fail the university entrance examination.

Persevere, or your will fail.

You must work hard, lest you should fail―for fear you may fail―for fear of failing.

the condition of receiving poor marks

What is the use of―Where is the good of―learning such things?

If you don't study hard, you'll continue to get poor scores.

Such a course of work and pleasure is too great a strain on your body

If you are to do well in school, you must study hard.

Persevere, or you will fail.

You'll have to study some to catch up with the others.

He has failed after all his labours.

With those results, you won't be able to go to university.

It is quite natural―It is no wonder―that, if he works so hard, he should succeed―Such a hard-working man ought to succeed.

What is the use of―Where is the good of―learning such things?

It is useless to learn such things

to give good results―give no result

Work hard, or you will fail.

Success in school calls for hard study.

The result is worse than I expected―disappointing―a disappointment―The result does not come up to my expectations―falls short of my expectations.

If he perseveres in his efforts,―If he keeps on as he has begun,―he will be sure to succeed.