Question

If someone has learned the Qur’an with tajweed, but still has a natural lisp, can they teach Qur’an?

Answer

If a qualified Qur’an teacher, more specifically a certified one (meaning they have an ijazah) has given them permission to teach, then they may.  The condition being that they can correct the defective letters on others, even though those letters are not pronounced correctly by the teacher themselves.  The must also explain to their students not to take those letters from him/her, instead they should take them either a tape of a good reciter, or the teacher with the lisp may point out a student in the class that has good pronunciation of these letters, and the other students should listen carefully how that specific student pronounces those letters.