The short version is that yes you would getting some professional input. (Although I would not suggest a child neurologist as first line, more like a child psychologist or neuropsychologist.)
What’s on the possibility list for that description with nothing else to go on?
Maybe he really can’t do better. Some kids have the social and verbal skills that make others think they are overall smarter than they are, but measured overall IQ is surprisingly lower than one would have thought.
Maybe he just does not care about school or academics. There certainly are kids who are smart and have focus but who are not interested in applying those smarts and focus on school subjects. When they care they do better. These kids are often accomplishing very interesting things on subjects outside of the class.
Of course ADD-I (Attention Deficit Disorder Inattentive predominant type) is on the list. Very high on the list. The sketch as presented is pretty much the classic presentation. As much as many kids are overlabelled as ADD many with ADD-I are never identified and just quietly fail. Teachers are pretty quick to identify the disruptive child as ADD, not the inattentive ones so well. They have no major issues with impulse control and do not act out. They are often often very creative and have great senses of humour. They have many strengths. But focus on any one subject for any length of time is not among them. They can even do fairly well in the lower grades if they are overall smart enough - using a third of their focus on the classwork at hand is enough - but they pretty quickly get to the point that they need to be using more of their focus on the single subject for a sustained time in order to not get lost when they get to middle school and beyond. Usually a parent can recognize a similar pattern in themselves or in one of their sibs.
Learning Disability, depression, drug use, frequent petit mal (absence) seizures … sure all part of the list of possibilities, even if the story as told so far does not suggest them to be very high on it.
Meanwhile the school skills focus should be on the skills and habits not the grades. He gets some token for having done some X amount of schoolwork per night whether it was assigned or not (not that much assigned then review or preview) and has to demonstrate evidence of having done it. Assignment book ideally signed off on by teacher and checked by you and him showing you where in his folder he has put the completed work. Many schools now have the assignments on line to. Tokens for those tasks too. Privileges such as electronic entertainment device time are earned with those tokens and the amount it takes is a negotiated contract.