the fact that you have to QUESTION whether the teacher is good or not already is your answer.
If you are not sure what your child needs to do, shouldn't there be a notebook indicating what was taught? You can record the lesson? Or you can call or email the teacher to find out what's the lesson plan and short term ,and long term goals for your child.
A good teacher is a teacher who can guide your child to the piano with enjoyment, and you should see your child always wanting to go to the piano to play something.
At the beginning, posture, learning the basics of the piano/keyboard, strengthening fingers, singing, learning do re mi, or C D E, and playing short little pieces with few fingers ......
my daughter also has a notebook showing what have been learnt in lesson such as which book, which page, what need to be paid attention, what skills are learning....etc. I will also talk with teacher after lesson to know her progress / whether my daugher is behaved or not....because my daugher sometimes will be lazy and not practicing well...i think teacher and parent need to communicate well.......