It starts with Jaiden.

She gives the orbs to Joel and Stone

After Joel became a teacher and have TS the blue orb.

After what Stone did,Joel took the orb from her and searched for a new student to take the red orb.

Thus found Nyoko

After a while they (TS and Nyoko) became teachers.

Then they found Chad and Aysel

They became teachers too

Of candy and Crosby

Then they became teachers too..

Of Cherry but she hasn't had the chance to have a blue orb partner.

Things how the line works. I guess.