When I'm struggling a little extra to focus or have a task that's particularly demanding of my attention, I turn to binaural beats. Binaural beats work by introducing two different sound frequencies in each ear. This causes the brain to produce a third "phantom" frequency made up of the difference in the initial two. According to a 2016 study in PLoS One, this phantom tone "can be manipulated for non-invasive brain stimulation."
Participants in a 2010 pilot study reported improvement with homework problems due to inattention after listening to binaural beats for three weeks. While the results concluded that there wasn't a significant reduction in symptoms, I, like the study's participants, certainly find an increased ability to focus for longer periods of time. However, if you have certain medical conditions, such as a history of seizures, you should consult your doctor before listening to binaural beats.