Shaykh Abdul Azeez ibn Baaz rahimahullaah in his Majmoo` Fataawaa vol. 13 pg. 259 was asked the following question:
Q: My mother cannot read or write, so it is permissible for me to read the Noble Quraan and pray supererogatory prayer and gift the reward of that to her? If it is not permissible then what are the acts for which I can gift the reward to her? May Allaah reward you with good.
A: There is not a legislated proof that indicates it is prescribed to dedicate the reward of prayer and reciting the Qur`aan to another person; whether they be alive or deceased. And the acts of worship are tawqeefeeyah (dependant upon textual evidence from Allaah or His Messenger, from the Quraan or the Sunnah only). Regarding worship, nothing is to be done except for those acts which the legislation prescribes.
However it is prescribed for you to supplicate for her and to give charity on her behalf, and that you perform Hajj and Umrah (major and minor pilgrimages) on her behalf if she is old and unable to make Hajj or Umrah.