We give volunteers review materials to help them brush up, and to be honest... even the best tutors have to Google things occasionally to refresh their memories

We give volunteers review materials to help them brush up, and to be honest... even the best tutors have to Google things occasionally to refresh their memories during a live tutoring session. :) But yeah, it does take some investment on the part of the volunteer if they haven't looked at a specific subject in 5+ years.