Write a letter to your younger brother advising him to be careful about studies.
I have received your monthly progress report today. I am shocked to note that you have failed in almost all the subjects. Your class teacher has informed me that you are neglecting your studies. You waste your time and are irregular.
It is not good on your part. You should attend to your studies properly. A student who gets careless and idles away his time in bad company is sure to fail and come to grief in the long run. It is time that you mend your ways and start working earnestly. I hope you won’t give me any cause of complaint now and show a much better results next time.