It's really common for students to thank their tutors at the end of the session and leave comments in the post-session feedback form saying how awesome the tutor was. Right now we're just sharing that feedback with the volunteers ad hoc, but we'd like to find a better system to share it regularly.
We're also planning to launch a volunteer favoriting feature for students later this year, which will increase the likelihood of students and volunteers who get along well having future sessions with each other. It's actually a commonly requested feature from both students and volunteers!