It can be frightening to have a downward shift in grades--and even harder to know what to do about it, since many factors can come into play. Finding a balance between friends, family, school and extracurricular activities is key; and certainly having more time to study can't be a bad thing.

Do you know why your parents are so dead-set against you withdrawing from these after-school programs? Getting to the root of why they object so strongly and giving them reasonable alternatives may appease them.

They may hope that your participation in these activities will give you a more well-rounded experience of life, but explain to them that your studies take time and concentration, which are not possible when you are obligated to attend so many meetings/practices, etc. Let them know you can pursue these types of activities on the weekends or, perhaps, one or two days during the week instead.

As for other ways to reduce stress, try to find things that do relax you. Do you have a hobby? Do you meditate? Swim? Make art? Try doing something relaxing a few times a week instead of staying after school for all these extra curricular activities, if your parents allow you to. By participating in something you chose to do when you feel like doing it--not something that feels regimented and obligatory--may help bring those stress levels down and allow you to better concentrate on your studies.

Good luck!