Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
You are obliged to observe fasting during the month of Ramadan, and be sure that you will have a matchless reward if you continue fasting while doing your exams.
In this regard, Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, states:
It is not permissible to break the fast for the reason you mentioned, rather it is haram, because it is not included in the reasons for which one is allowed to not fast in Ramadan.
Moreover, it should be noted that fasting in Ramadan is an obligation upon every accountable Muslim, and no one is excused from fasting at the time of fasting except for those who have valid excuses, who are granted the concession of being allowed not to fast, such as the sick, travelers, pregnant and breastfeeding women, the very old, and those who are forced to break their fast.
Allah Almighty knows best.
Source: www.islamqa.info