Косвенная речь "I left school at fifteen." Her letter said that she school at fifteen.

Her letter said that she has left school at fifteen.

Teachers usually advise their pupils to think about compulsory subjects. They recommend teenagers to make a list of skills they have, to correlate their interests with the subjects they can study and to train key skills that will help in any work. Parents recommend their children to choose which qualifications they need and to get information about different courses. Parents often advise their children to find and tell 
them to find out more information. Teachers advise teens to think of making decisions 
but to consider all the opportunities and to deside what they really want, besides they 
recommend teens to discuss their choices with their parents. Думаю так

Teachers usually advise their pupils to think about compulsory subjects. They recommend teenagers to make a list of skills they have, to correlate their interests with the subjects they can study and to train key skills that will help in any work. Parents recommend their children to choose which qualifications they need and to get information about different courses. Parents often advise their children to find and tell 
them to find out more information. Teachers advise teens to think of making decisions 
but to consider all the opportunities and to deside what they really want, besides they 
recommend teens to discuss their choices with their parents.