Nope, you're not the only one (but I sure hope we're not the only two!) DS was better in arithmetic in kindergarten than he was at the end of first grade. I don't know exactly why, but I think the constant repetition of "easy" math either made him forget what he already knew, or made him lose confidence in his math abilities.
And FWIW, DS barely passed any of his timed subtraction tests this past year (in 2nd grade), even though he was accelerated to 4th grade math. He despises timed tests, and basically shuts down and answers only a few questions. I know he knows how to subtract, he just can't always do it on command when he feels pressured.
