A CESSNA 120, N9058Y, & A CESSNA 152, N65599, COLLIDED IN MIDAIR IN THE PRACTICE AREA FOR EL MONTE, CA. ARPT. THE TWO AIRCRAFT HAD DEPARTED THE CONTROLLED ARPT WITHIN THREE MINUTES OF EACH OTHER. BOTH HAD ONE INSTRUCTOR & ONE STUDENT ABOARD. THE CESSNA 152 WAS STILL OUTBOUND IN A NORTHERLY DIRECTION & THE CESSNA 120 HAD CALLED THE TOWER FOR LANDING INSTRUCTIONS WHEN THE COLLISION OCCURRED. THE CESSNA 120 BROKE UP IN FLIGHT & INJURIES WERE FATAL TO BOTH PLTS. THE CESSNA 152 MADE A SUCCESSFUL EMERGENCY LNDG. ACCORDING TO THE INSTRUCTOR & STUDENT IN THE CESSNA 152 THE ACFT WAS LVL AT2000 FT MSL, HAD JUST COMPLETED A LEFT TURN & WAS ABOUT TO BE IN A RIGHT TURN WHEN THE STUDENT, FROM THE LEFT SEAT, SAW ANOTHER ACFT IN HIS EXTREME RIGHT FIELD OF VISION, APPARENTLY FROM ABOVE. THE WINDSHIELD OF THE CESSNA 152 WAS SHATTEREDBY THE EMPENNAGE OF THE CESSNA 120, WHICH SEPARATED IN FLIGHT. THE INSTRUCTOR IN THE CESSNA 152 WAS A NEW INSTRUCTOR & NEW TO THE AREA. TWO VETERAN PLTS WERE ABOARD THE CESSNA 120, WITH ONE CHECKING OUT IN HIS NEWLY PURCHASED ACFT.