I would concur with what tired has said here, this is one for the professionals however I ask why so much pressure from you ..he is only 6 year old that sends up a red flag in my head I sense there is more going on ...
I wasn't too concerned until I read about the cyst on the frontal lobe. The only reason that rings warning bells is because people with frontal lobe problems often have memory problems- i believe primarily short term which is what he is demonstrating.
If I were you, I would make an appointment with a neurologist. While the cyst is "harmless" or benign, if it is pressing on the brain, it can affect it. And the location of your son's cyst could possibly cause memory problems. Frontal lobe can also effect emotions greatly. Neuropsychological testing can reveal if the brain's function is being affected by the cyst.
Even if it is not the cyst, he may have short term memory problems. I have had students with this problem in the past. Child study team testing detected it, and with a little help, the child began to do much better.