Every teacher teaching a 16 and under must have a University degree. That every teacher should have a formal Post-Graduate teaching qualification, or that they are working towards that qualification. In times of need, there are teachers with a University degree, but without a Post Graduate qualification, teaching your child. In that case the responsibility lies with the Head to ensure that the teacher in question can teach effectively. Knowing your subject is only the start when it comes to teaching.
Some schools use Cover Supervisors. These members of staff are meant to stand in for a qualified teacher, and support the class with work left by a teacher. While some do have a teaching qualification, or a degree, most do not. Effectively it means that an unqualified person is supporting your child. Now before I am ambushed by a mass of Cover Supervisors, I do know that some do an amazing job. However, I have that teaching qualification. I worked hard to become a teacher. And I would be ridiculing my position, I would be stating that I didn't need a qualification to become a teacher if I agreed with the use of Cover Supervisors. It is far cheaper to a Head to use a Cover Supervisor than a qualified teacher. However it is YOUR child that will be influenced. I leave you to make up your own mind.
And Supply teachers. Do not consider that these people are not real teachers! They are! Qualified people that do not have, or choose not to have a permanent position in a school. Most do have a Post graduate qualification, but some exist with just a University degree. If your child has a Supply teacher, make sure that your child is still being taught, still working on the subject that the absent teacher would have taught. Ask your child, and if not happy ask the school! Most good Supply teachers are aware that they are obviously interrupting the continuity that an existing teacher provides, and part of the position is to provide as little interruption as possible.
At this point I should mention teaching staff turnover. The better the school the less likely teachers are to leave, and the more continuity it provides to your child. Ask the Head about the percentage of staff turnover from year to year. The answer will provide a useful tool for you to decide which school your child should attend.