Hi, flowersfamily!

While lower than average, PSI=83 is still within the normal range. It could certainly be causing a processing bottleneck for him, though. My DD9 has similar problems with writing and spelling. Her oral spelling is much better than her functional spelling, too. She has been diagnosed with a LD which seems to be related to visual/motor integration.

You may want to get private testing and get some recommendations from the psychologist as to what may help him. More time is probably one thing, but there may be others.

One thing the psychologist recommended for DD is that she learn to type. Typing her writing homework has really helped her. You may also want to read about dysgraphia. There are a few threads here in the 2E section about that.