As the parent of a child with ADHD, you may already be aware of certain times of day that are more difficult than others. If your child has begun taking a stimulant medication, you may notice fluctuations in her attention and behavioral control throughout the day as each dose of medication begins to take effect, works well, and then wears off. With stimulant medications, effects such as behavioral rebound (a short period of irritability or moodiness as the medication is wearing off in about 4, 8, or 12 hours) may lead to difficulties at around dinnertime or bedtime that had not generally occurred before. You can help your child adjust to these changes by observing how and when her emotions and behavior tend to fluctuate each day and arranging her schedule as much as possible to accommodate these ups and downs. If you know, for example, that she is usually somewhat unsettled and irritable for a half hour after her arrival home from school, schedule her homework for after that time. If her medication suppresses her appetite at certain times during the day, schedule meals to avoid these periods. Take special care to prepare her for transitions between activities because these are likely to be especially difficult times for her.
Another issue to consider is the way a specific length of time can sometimes feel to your child with ADHD. For a child who struggles with managing her behavior or retaining focus for more than a few minutes at a time, tedious, repetitive, or boring activities can seem exceedingly long and soon become absolutely unbearable. Forcing your child to participate in such an activity (requiring her to sit still for long periods while you chat with a friend, introducing her to clubs or groups that involve little physical action and too much down time, expecting her to pick up all the toys at once in a disorderly room) will probably only lead to failure and the probability of subsequent punishment. Even fun activities can be strenuous in the same way. For example, baseball, which includes long periods of inactivity while on the field, may not be as good an activity for children with ADHD as soccer, which has a much faster and continuous pace. By avoiding such situations or breaking up activities (including homework) into short chunks of time, you can help your child experience success as she struggles to manage her responses. It may also help to let your child know ahead of time how long a particular activity will last, and even to place a timer in view to help her awareness of how much time has passed. If she knows she has already been working on her homework or practicing the piano for more than half the allotted time, she may be able (with your support and coaching) to continue to the end.
Source ADHD: A Complete and Authoritative Guide (Copyright © 2004 American Academy of Pediatrics)