Help your teen develop a schedule!

Try to find ways to make them feel positive about what they are doing. Encourage them to work however it suits them, maybe that's in the garden, or with their music on if it helps them. Make sure it's what works for THEM, not what works for YOU!
A positive emotion opens a gateway in our brain to the long-term memory and is crucial if they are to learn and remember. A negative emotion closes the gateway to learning, and just allows the bad feeling to be remembered...think about it...what do you remember about your worst subject compared with your favourite things?
Avoid being critical. Give them choices and encouragement, praise and recognition for what they do.

If you are having a tough time with a subject check out Kahn Academy. Awesome free videos and practice problems for FREE on various subjects. AWESOME SITE!!

Sorry error. It's Khan Academy not Kahn Academy.