It would be nice to start after learning some basics on Scratch.
A student should know basic concepts: variables, conditions, loops and basic algorithms. Also know what multiplication, division, remainder of a number, fractional numbers are.
To attend classes a student needs to have good computer skills:
use browser, open new tabs there, download and install files on a computer, create/rename folders, know the keyboard layout, use hotkeys, type and use computer mouse confidently.
For students from 10 years old.
For classes it is needed to have a text editor installed (Notepad++, Sublime, etc)