Considering the purpose of this screen is to require "users to identify whether they are a teacher or parent," one approach would be to spell it out in plain english, simply say:
To continue, please select what best describes you:
[ I am a Parent ] [ I am a Teacher ]
This approach is a bit wordy, but makes it very clear what is expected of the user.
I have no idea how this fits within your wider context, but assuming the majority of usage is by parents, consider somehow removing this choice altogether in favor of streamlining the user flow for the parents, then providing an alternative flow for teachers. Once again, this may or may not work depending on your wider flow, but if it has potential to reduce the amount of choices a user is required to make, it's usually worth at least looking into to see if it makes sense.