Within 8 working days of arrival all non-EU students intending to stay in Italy for more than 90 days must apply for a residence permit for study purposes (“Permesso di soggiorno per motivi di studio”). The residence permit is issued by the local Police Department – “Questura-Ufficio Immigrazione”.
http://www.poliziadistato.it/articolo/10716
Students can apply directly for the residence permit for study reasons, obtaining a kit from any qualified post office (Poste Italiane – Sportello Amico). The kit is an envelope containing the forms and instructions on how to fill them in. We advise you to go to the authorised C.A.F. office where they will help you start the procedure of obtaining the residence permit.
The International Relations Unit will provide assistance for the fulfillment of the residence permit procedure.