C172 Instructor pilot reported safely landing straight ahead shortly after takeoff because the engine was not developing full power.

Narrative

After being cleared for takeoff on Runway XX at ZZZ; my student and I taxied onto the runway; lined up on the center line; and advanced full power. After our airspeed was alive; we rotated and started our initial climb. Upon reaching about 50 feet AGL both my student and I agreed that we were not happy with how the aircraft was performing. The tachometer was indicating about 2000 RPM which is low for the takeoff power setting (Full throttle). The aircraft felt like it was not producing full power for us. There was no indication of engine roughness or anything like that. I made the quick decision that there was enough runway remaining and that we were going to land straight ahead on Runway XX at ZZZ. We immediately reduced the power and transitioned to a normal landing on Runway XX.Once we touched down and came to a stop we contacted ZZZ Tower to get clearance to taxi clear of the runway. The Tower asked the reason for the aborted takeoff; and we informed them it was because of a lack of RPM on takeoff.We cleared the hold short line of Runway XX on Taxiway and contacted ZZZ Ground for taxi instructions. We requested to taxi back to the runup area for Runway XX to further diagnose the issue we had just encountered. Once we were in the runup area we did a full-throttle runup and only saw 1950 - 2000 RPM. I even tried leaning the engine to different mixture settings to see if that would change anything.At that point; we decided to taxi back to the flight school and have maintenance take a look at the aircraft.