This blog post
from Alton Towers about their preparations for this year's school trip season contains the following, potentially suggesting that students will get access to Early Ride Time:
This year, the team has also arranged for schools to enjoy an extra half-hour on park before it opens to the public to help them make the most of their trip and enjoy even more thrills.
Can't help but feel this will be a bit pointless if there are going to be "thousands of children" showing up, especially if ERT attractions continue to struggle to open on time. It will also perhaps not be best received by those usually entitled to ERT who are visiting during the coming few weeks, although I suppose you could say more fool them for planning their visit for then.
Even though this is being positioned as a perk, I wonder if part of the reasoning is so they can start admitting schools as promptly as possible, so as to avoid chaos and crowds in the entrance plaza at the start of the day.