My dd2 left Reception having acheived all 8's and 9's on her report.
She was above average in all aspects of the curriculum (apparantly).
Throughout Y1, she performed averagely. Our school grade progress A (above ave) B (ave) and C (below ave) - her end of Y1 report read largely B's with a couple of A's.
We were a little disappointed, but figured she was happy and acheiving so it didn't matter.
The other very important factor, we felt, was that she didn't really have any connection with her Y1 teacher. She was perfectly nice but she didn't 'get' dd2. Again, no worries, there are always going to be parent/children combinations which don't work. Thats life.
Anyway, dd2 had a much better year in Y2 and comments were very much back to what they had been in Reception. She loved her teacher, and her teacher seemed to have a genuine fondness for her. She completed her SATs back in May (all 3's) and her end of term report read all A's.
I guess the point to my post is that there are a number of factors that affect your child's seeming progress, and that children's learning isn't steady, it peaks and dips.
I'm sure your ds will be fine ...and he sounds like a real sweetie 