(2) The data reflected more on the performance of the students than the performance of the school.
I would change this sentence.
Here is how I would writie it.
The data reflected the performance of the students more than the performance of the school.
or: The data was more a reflection of the students' performance than the school's performance.
(1) The chairman welcomed members to the meeting.
It would be a good idea to specify which members the chairman welcomed here. Are we talking about members of a committee?
The chairman welcomed the committee members to the meeting.
In any event, I believe "the" should be placed before "members", as the sentence would be making reference to certain or specific members I would think.