You do a test (11+ based), shadow a staff member and then get interviewed by 2 people, it is fairly short, and is mainly about your availability and time management.
J'ai passé un entretien chez AE Tuition (Slough, Berkshire, South East England, England)
Entretien
the process involved an interview (standard with relevant questions), a test (to see if you can cover what’s taught and do it yourself) and it also had a section where you shadow a current assistant and the work they do per shift