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, know the keyboard layout, use hotkeys, type and use computer mouse confidently.
For students from 10 years old. However, children under 13 need to take a test for signing up