'Effective Feedback'

What is 'effective feedback'?

Should effective feedback be a grade, a mark or a phrase like 'Good', 'Excellent' or 'Well done'?

All of the above is FEEDBACK, but may not be effective one...

Yesterday, I received student evaluation from two groups of students. One is from in-service NSS course and one from BEd students. I was elated as both groups of students gave me very positive feedback which could motivate me to do better and encourage me to continue my good practices. However, I realize that the in-service group gave me some very weird comments such as:

"In this short course, there should be no assignments."

"The course should not be held on Saturdays."

"I think this tutor is young and inexperienced to teach us." (My immediate response is I am not very young.)

What do you think? The above is all feedback but not feedback about how to improve teaching and learning. The feedback given by the teacher participants can't inform me how to improve my teaching nor how to facilitate better learning in this professional development course. Instead, they are purely 'personal' grievances towards the course. And also I would say the last comment is a little bit offensive though I took it as a compliment!! I think being a professional teacher, we should learn how to give effective feedback which can help improve our teaching as well as enhance effective learning.