PA28 flight instructor reported a near midair collision with a cessna on short final.

Attributes
ACN	1561873
Time
Date	201807
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Operating Under FAR Part	Other 61
Flight Phase	Final Approach
Route In Use	Visual Approach
Flight Plan	None
Aircraft 2
Make Model Name	Cessna Single Piston Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Person 1
Function	Pilot Flying
Qualification	Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 140 Flight Crew Total 540 Flight Crew Type 315
Events
Anomaly	Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance
Miss Distance	Horizontal 0 Vertical 100

Narrative:

I was conducting take off and landing practice with a student; staying in the traffic pattern at ZZZ. At approximately 500 AGL; on short final for 17R my student was flying when I noticed a cessna at our altitude on a collision course. At the same time the TCAS reported the traffic and I took controls to emergency descend below the traffic. At that time ZZZ tower reported traffic alert and that he was unaware of where that traffic was going. I completed a normal landing and ended the training flight.

Original NASA ASRS Text

Title: PA28 flight instructor reported a NMAC with a Cessna on short final.

Narrative: I was conducting take off and landing practice with a student; staying in the traffic pattern at ZZZ. At approximately 500 AGL; on short final for 17R my student was flying when I noticed a Cessna at our altitude on a collision course. At the same time the TCAS reported the traffic and I took controls to emergency descend below the traffic. At that time ZZZ Tower reported traffic alert and that he was unaware of where that traffic was going. I completed a normal landing and ended the training flight.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.