It will depend upon the National law of the country where the Flight School operates. When you change from JAA to EASA then assuming the school is in an EASA State NCO GEN.135 will apply; when it becomes EU law:
NCO.GEN.135 Documents, manuals and information to be carried
(a) The following documents, manuals and information shall be carried on each flight as originals or copies unless otherwise specified:
(10) current and suitable aeronautical charts for the route of the proposed flight and all routes along which it is reasonable to expect that the flight may be diverted;
It does not say they have to be paper charts but if the PC fails you become illegal unless you have a backup!