Is it better not to take payment for teaching the Quran by heart, or to take it and donate it, especially when one is in debt and a parent has instructed one to take the payment?

It is better to teach the Quran seeking the Face of Allah [i.e., for His sake], but taking a wage for it does not invalidate the reward of the deed, especially if it encourages parents to send their children.

As for obeying the parent in determining the teaching wage, it is obligatory if it does not involve disobedience to Allah, and if the parent has a valid purpose, and if no harm results to the child from it.

It appears that teaching the Quran for free is better than taking a wage and then giving it away as charity.