Determining sample type

Hello everyone

I'm currently trying to determine my sampling type and I'm still unsure about it. For context my research supervisor emailed 3 schools to participate in the research study. Of which the participant inclusion requirements was for them to be post 16 years old, undertaking science related a levels and/or btecs. Once the schools confirmed they'd participate the students was sent an email invitation to complete an online pre and post intervention questionnaire. No reward was offered and participants could opt out however the word voluntary wasn't mentioned on either letter.

I'm leaning towards it a convenience sample but I'm still not sure and if the population is just an accessible population rather than target.