Hiya, I've been working at Explore - the Barking branch for 15months now. I started in Sixth Form. Honestly don't worry too much about your grades as long as you got C's in Maths and English - in training they go through the various curriculum methods to teach you.
Interview wise: they ask you about relevant experience working with young children, why you'd want the job and then give you 2 maths questions in which you pretend you're the tutor and you have to explain to the manager (who pretends to be a child) how you would go about answering the question.
Tips: Explain the question on paper and pass the pen to the "child" and get them to fill in the answers. They like that.
NOTE: I got given adding fractions as one of mine, I checked with the manager that I was doing it correctly and still go the job. Let's just say I never forgot how to do it again haha.
As for pay rate it's about £5.45 if you're under 18 then it increases to £5.75 I think. Then you get a regular appraisals every 3 months in which a pay rise may take place. I can't remember what it is for those already over 21.
Good luck guys.
P.S Inductions are usually 3-hour days in which you look at the levels of software on computer, and begin to learn how to write session notes.