Okay, just to clarify, I don't answer each of these questions for each of my characters, but this is a list of things I look at when I'm trying to develop their backstory so that I can capture their personality on the page.
Gender - not that you don't already know what gender your character is, but be sure you really consider how gender affects worldview. Boys walking into a situation have very different reactions and notice different things than girls do. Frex, in middle school, a boy walking into the cafeteria on the first day of school might be wondering who is going to trash can him or who he could beat up if he had to. A girl, however, might be looking for who seems the friendliest or which social cliques to approach/avoid.
Family’s social status/income level - because poverty greatly affect worldview
Any ethnic background or influences?
What is their family dynamics? Parents married, divorced, single? Siblings? Birth order?
What sort of student is the character?
How popular are they at school?
Who is his best friend?
Who is their worst enemy?
Do they have any hobbies? If so, how did they come to those hobbies?
Are they athletic? Good at sports? If so, which ones. If not, how does that affect their life?
What is the character’s most treasured possession?
Do they have any superstitions?
What is their general attitude toward life? Optimist? Pessimist? What went into forming that attitude?
What are they afraid of?
What are his hopes and dreams? Both immediate and long term.
What does he long for?
Does he have any food likes or dislikes?
What about pets?
Is there anything he feels guilty about?
What is his favorite book, TV show, or computer game?
What is his relationship with technology? Do they have four TVs? No computer? A cell phone at age 10? An email account? (in historical or fantasy novels, this question is a whopper as it encompasses the other world you're building into your story.)
What are his character strengths?
What are his character flaws?
What about Quirks?
Does he have any physical weaknesses? Uncoordinated, asthma, small for his age, etc.