My comments:
1. What factors do you consider important in causing mixed ability? Put these in order of importance for you:
I consider that all these factors are important in causing mixed ability.
previous exposure
learning style
motivation
attitude
personality
aptitude
2. "Every group is a mixed-ability group." Do you agree with this? What are the implications of this statement for teachers?
Yes of course, every group is a mixed-ability group, I definitely agree with this. The implications of this statement for teachers are that he/she has a big challenge to make that all the students learn and work. They have a lot of students in each group with different kind of learning style, previous exposure, etc. so teachers have to do activities that contain actions for all their students.
Teachers can practice in the groups the collaborative job. Teachers have help students that have more experience or knowledge of the topics.
Greetings,
Graciela Ávila