How many students do you hope to get to fill in your questionnaire?
How many teachers will you interview?
Do you want particular types of students?
Male/female, students who are performing well or struggling, students with good strategies, a selection.
For teachers, do you want experienced, newly qualified, or teachers with a range of experience.
If for example you are interested in teachers’ use of ICT, do you want to recruit mainly teachers who are enthusiastic about technology or include those who don’t like it?