Like Astrolady said, they don't have to be in a specific grade.

From the ATO website:
A child or an independent student satisfies the schooling requirement for each six month period, commencing 1 July or 1 January, if they:
  • are registered or enrolled in a primary or secondary school course provided at an educational institution such as a school or TAFE, or
  • are registered or enrolled with the education authority of their state or territory as a home schooled student, or
  • are registered or enrolled in a course of study or instruction which the Minister administering the Student Assistance Act 1973 determines that the Education Tax Refund applies for, and
  • attended the course of study or instruction, or received the home schooling, at least one day in a six-month period commencing from 1 July or 1 January.
Where a child or independent student starts or leaves school during the year, or for other reasons only satisfies the criteria for one half of the year, you or the independent student will be entitled to claim the refund for that half of the year.