Probably one of the daftest ever PPRuNe questions. No of course you can't log the time you spend sitting on the ground watching your students fly!
Student pilot-in-command (SPIC) flight time is that during which the flight instructor will only observe the student acting as pilot-in-command and shall not influence or control the flight of the aircraft. SPIC hours can only be accredited for graduates of Integrated Courses for ATPL (A)/(H) and CPL(A)/IR.
In other words you have to be in the aeroplane watching the SPIC bumbling about to claim any P1 time - if you elect to take control or otherwise 'influence or control the flight of the aircraft', then the student will have to log it as Pu/t.