Understand that teenagers learn differently and that they should not be punished or scorned for this fact. Some teens may learn well from doing book research, while others absorb knowledge more effectively by watching instructional videos. Help teens find the best way of learning for them. This will motivate them by letting them know that they are not an outcast just because they have a different style of learning.
Demonstrate to your teenager how to manage time so that the feeling of being overwhelmed won't cause him or her to lose motivation. Managing time is a skill that is often not developed naturally by kids because when the teen was younger there weren't so many things to keep track of. Help your teen create a schedule that allows plenty of time for things like homework and studying, but doesn't conflict with other planned activities.
Aid your teenager in addressing the fears that he or she has; this fear is often what's causing the lack of motivation. Realize that a teenager who seems to have no motivation to play sports might actually be a teenager who's afraid of failing or playing in front of large crowds. Keep in mind that a teenager's fear can be caused by several things, such as low self-esteem or an inability to fit in with peers. One way to help teens face their fears is by explaining to them that nobody goes through life without failing at something.
Communicate with your teen and his or her teacher on a regular basis. Ask your teen things like what type of schoolwork he or she is currently doing. This can motivate a teen by showing him or her that you care enough to stay involved.