On July 13, 2017, about 2320 eastern daylight time, a Cessna 172M, N80457, was substantially damaged during a forced landing to a road near Key Biscayne, Florida. The flight instructor was not injured and the private pilot receiving instruction sustained minor injuries. The airplane was being operated under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Night visual meteorological conditions prevailed at the time and no flight plan was filed for the flight which originated from Miami Executive Airport (TMB), Miami, Florida, about 2055.The flight instructor stated that during the preflight inspection, both fuel tanks were visually inspected and also checked using a dipstick, and each tank contained about 15 gallons. The flight departed TMB with the fuel selector on the "both" position, and flew to Fort Lauderdale Executive Airport (FXE), Fort Lauderdale, Florida, where the private pilot, who was receiving instruction for an instrument rating, executed a practice instrument approach that terminated with a full-stop landing. The airplane remained on the ground for about 15-18 minutes with the engine operating, then departed and flew to Palm Beach International Airport (PBI), West Palm Beach, Florida, where the private pilot executed another practice instrument approach, which terminated with a missed approach, and holding practice. About 2215, the flight instructor elected to return to TMB and requested visual flight rules flight following from air traffic control (ATC). The flight proceeded south, east to the coast, and then south along the shoreline. While flying near Key Biscayne with the engine operating between 2,300 and 2,350 rpm, the mixture control full rich, and the fuel selector on the same position it had been since the initial takeoff (both), the engine sputtered for about 2-3 seconds, lost power, then increased briefly to 1,500 rpm, before losing power again. The private pilot reported the left and right fuel gauges at that time were indicating in the lower red arc and between 1/4 and 1/2 capacity, respectively. Attempts to restore engine power consisted of moving the fuel selector to each fuel tank position, and checking the magnetos on each respective position, but engine power was not restored. The flight instructor declared an emergency with the ATC controller and requested assistance from emergency equipment. While descending for a forced landing to a road, the airplane collided with tree branches, and then a light pole, and came to rest within 25 to 30 ft of the touchdown point on the road. According to a Federal Aviation Administration inspector, there was no evidence of fuel leakage or a breach of either fuel tank. Less than 1 gallon of fuel was drained from the left fuel tank, while about 10 gallons of fuel were drained from the right fuel tank. The airplane was recovered for further examination at a later date. Examination of the airplane following recovery revealed the right fuel tank strainer, part number 0422130 was nearly completely blocked by organic material.