A321
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2.7
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Separated Traffic; Air Traffic Control Issued New Clearance
Aircraft
Aircraft X departed and was climbing on the SID. Aircraft Y subsequently departed on the same SID.  When Aircraft Y's tag acquired they were 2.8 miles behind and only 10 knots slower over the ground than Aircraft X. Having encountered this scenario numerous times before; I immediately utilized the shoutline to the Local East controller and assigned 3;000 feet to Aircraft Y. Since Aircraft X had already vacated 3;000 feet; I knew I would at least retain vertical separation.  Within 10-15 seconds Aircraft Y had accelerated to and exceeded Aircraft X's ground speed. Within one minute of Aircraft Y's departure they were showing 30 to 40 knots faster than their preceding traffic. Aircraft Y was subsequently vectored and climbed appropriately in-trail of Aircraft X and both left our airspace without further incident.This is a common problem that we experience with A321 departures. I do not know why this specific aircraft type climbs out so differently; but it is common knowledge at the TRACON.  Tower does not seem to consistently take into account the performance of A321s on departure. Without my anticipation of the problem and action to retain vertical separation; there would have been a loss of separation.The Letter of Agreement (LOA) with Tower should be changed to exclude the use of pilot provided visual separation and require the provision of additional spacing to account for the lackluster performance characteristics of A321s' on departure.  I would recommend a provision of 4 to 5 miles between an A321 and subsequent departures.
A Departure Controller reported an A321 departing climbed at a much slower speed than a trailing B737 requiring them to vector the B737 away to maintain separation.