I feel this is the most common factor that haunts all the parents in the world, especially when we are in this competitive world like todays.
I would suggest couple of things for you out of my personal experience,
1. We should first understasnd what the kid thinks and why is he reluctant on studies.
2. Is there any thing distracting him, like playing, environment in home or school,
3. Is he being afraid of not understanding the subject and trying to ignore the same.
4. Is he comparing himself to others and getting to a conclusion that he cannot do wht others are capable of doing.
5. Is he reluctant towards all the other things or only studies.
Once you have noticed and studied all the above said things, then you need to counsel the child and make him understand what are the disadvantages if we dont study and get up to the mark, we should site him examples from our daily life showing him or explaing him what happens if we dont study, who will take care of his parents if he doesnt stusy and become a good person,
We should also note that the changes will not come overnight, is he been so since beginning or is his behaviour is changing recently, since the boys grow they get attracted to different things, we should spend more time with them to understnd thier world.
Some parents resort to sending kinds for more tution hours thinking that any ways he is not studying at home so let us send him to tution atleast he can study there, I feel this is complete misconception, we should allow more and more home study hours, so that we make sure the child is not pretending to study.
TV is one of the most dangerous thing to beat, if the child is addicted to TV, then we have to make him undertand the drawbacks of the same, and ristrict his timings,
Lastly as Chanakya said spare the rod and spoil the child, we should also make him understand that punishments are near if he is not being obidient towards studies.