All perfect praise be to Allah, The Lord of the Worlds, and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Fasting is a pillar of Islam that Allah has prescribed to all Muslims. He says in this regard(what means): "O ye who believe! Fasting is prescribed to you as it was prescribed to those before you, that ye may (learn) self-restraint,"{Al-Baqarah/183}.
The Noble Quran has clearly stated the excuses which allow someone to break their fast in Ramadan:" (Fasting) for a fixed number of days; but if any of you is ill, or on a journey, the prescribed number (Should be made up) from days later. For those who can do it (With hardship), is a ransom, the feeding of one that is indigent. But he that will give more, of his own free will,- it is better for him. And it is better for you that ye fast, if ye only knew."{Al-Baqarah/184}.
In conclusion, studying for exams in Ramadan isn`t a valid excuse for a student to break their fast. It is imperative that he/she starts their fast and do their best studying for exams. However, if they experience extreme hardship during day time, then they may break their fast. We pray that Allah, The Exalted, grants success to all students. And Allah knows best.