Sometimes adults may have an undiagnosed learning problem. For example, processing of iauditory information may not have been picked up in a quiet female who was well-behaved in her middle and high school years. It may become very apparent during continuing education classes when all the information is presented orally and she just "doesn't get it". This actually happened to me. My boss asked if I did drugs in the 70s, etc. (No!) but it led me to discover differnt learning styles, etc. I discovered I had a really high iQ but that processing disorder made me function much lower until I learned how to work around it.
