Is it permissible to buy gifts for only the outstanding students from money collected from students of a study circle, and is that considered gambling?

The money taken from the female students is not considered gambling as long as the intention is to donate and support the Qur'an memorization circles, and not to wager. If it is for the purpose of competing to win a prize, then some scholars have permitted competitions in knowledge and receiving prizes for them, even if some competitors contribute financially. Therefore, there is no harm in collecting these funds and spending them as mentioned.