The hearing something then saying something different sounds like a red flag to me. Poor auditory memory is another. In our case asking DD to do mental maths is an impossibility - she needs to hear the question at least twice and have time to write it down before she can think what the answer is. Haven't cracked times tables yet either . In our case it was only a mild problem in one out of four things they tested, so we had a list of recommendations for the classroom teacher to follow (seat her near, check for understanding, limit environmental noise). Good pediatric speechies can help too, I'm going to take DD to get assessed again next year (he had some work when she was younger) - she's older now and hopefully will learn a few new strategies that way.

You will have to do some research, it requires special equipment that not all hearing testing places have. We had ours done by a regular audiologist that had the equipment. I found out about them after I resorted to asking for parenting support thru the local govt cos I was at my wits end at the time. Perhaps start by discussing with your GP and find out what's available in your area, or an organisation like SPELD (google) might have some info in your state.