For the avoidance of doubt, on the part of the OP and any other student reading this........
So, NOT for use while the Instructor is with you.
On initial contact, student pilots who are flying solo shall use the callsign prefix ‘STUDENT’
1. Once acknowledged, it will not normally be necessary for student pilots to use the prefix in subsequent transmissions until making initial contact with other ATSUs, unless they feel they are being instructed to do something with which they are unfamiliar.
1. Although intended primarily for use by ab initio students, the prefix shall also be used in other circumstances where, for example, the holder of a valid licence is returning to flying practice after a significant absence and is undergoing renewal training involving solo flight conducted as a student under the supervision of a flight instructor.
15 November 2012