I know your studies (at school) are hard, but keep working hard.
I know school is tough right now, but keep at it.
ーI know your studies (at school) are hard, but keep working hard.
「勉強大変だと思うけど、頑張ってくださいね」
keep working hard で「頑張って」
ーI know school is tough right now, but keep at it.
「今、学校が大変だと思うけど、頑張ってくださいね」
keep at it で「頑張って・（何かを）頑張って続けて」
ご参考まで！
カナダ 
