Large Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 26
Distraction; Time Pressure; Situational Awareness; Communication Breakdown
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance
Human Factors; Procedure
Aircraft X was on approach to 25L at 3;200 feet following Aircraft Y at 1;000 feet 5.6 miles ahead.  I asked Aircraft X: Traffic 12 o'clock; 5.5 miles a heavy Airbus do you have it in sight?'  Aircraft X said he did.  I told Aircraft X to 'Follow the heavy airbus to the same runway; cleared visual approach Runway 25L; caution wake turbulence.'   Aircraft X responded cleared visual approach.  I corrected him saying 'Follow the heavy airbus; cleared visual approach Runway 25L.'  Aircraft X responded 'Check the wake turbulence' or something to that effect.  By the time I could have responded again; Aircraft X was 4.9 miles in trail.  Aircraft X subsequently landed without incident.The frequency discipline of pilots have really degraded in the last few years.  Apparently; the ability to read back a clearance is something that is not stressed in training; nor followed up by the airlines.  I cannot tell you how many times I encounter a situation; in particular one involving wake turbulence; where the pilot sees the preceding aircraft; but does not read back the clearance as issued; thereby invalidating the wake turbulence separation and leading the controller into a loss of separation.  It is important that pilots read back clearances exactly how we state them.  That is why we use standard phraseology.  This needs to be stressed vehemently to the pilots through their associations and companies.  It may be a point of semantics; but words are the tools of communication and ATC and without their correct usage; controllers are at a distinct disadvantage; if not totally impotent.
A Southern California TRACON (SCT) Controller reports of read back that was a caused an operational error. The pilot did not read back key words and because of this the Controller is charged with a loss of separation.