If you can recreate a similar situation in the place you study, you will find it much easier to begin studying and to continue studying when other students would be prepared to stop. Before you start an assignment write down the time you expect to finish. This step requires no time and will help you to focus your study efforts. Keep records of your estimates and the actual study times. The ability to concentrate varies with the individual.
Some persons seem to have phenomenal natural gifts to concentrate on specific tasks.
Most of the rest of us are forced to cultivate that skill. If you enjoy a football game on television, you find it easy to devote your attention to the game. Time even seems to pass faster. If you think that a particular chapter in your reading will be boring, you are sabotaging your ability to concentrate. So try to find, somewhere within you, an interest in what you are reading.