8-year-old's performance at school doesn't match what we see at home

ETA: Thank you everyone for your advice. The teacher has given me more feedback that indicates my son is behind in some aspects of reading comprehension, and we will be working at home with lots of reading time and Lexia practice to get back on track. I'll be able to get more details during parent-teacher interviews in two weeks and I'm planning on trying to take some writing samples in for her to compare his at-home work with his classroom work. Thank you all again!

I'm waiting on a response back from his teacher, but it seems clear (at least to me) that my son's ability to do things at home seems higher than his actual performance at school.

At school his assignments are written sloppily, and look like they could have been written by a kindergartener; when I quiz him on his spelling each week before the test day, his printing is nice and neat compared to the sloppy list in his planner. The writing samples look like they could be two different kids!

I just got a letter from his teacher that, based on his performance with the Lexia program, he is quite behind in several aspects of reading. This was news to me, as his previous year report cards always said he was at grade level, and we just sat down and he read aloud to me a book that was clearly somewhat challenging but he that he could read with some fluidity too...a book that is rated between his grade and the grade level above him according to Scholastic.

So...what now? His school performance makes him look like he's behind in reading, writing, organization...and at home he does it all just fine?