Thanks for the info regarding Ernest Robertshaw. His attendance figures might need a little head-scratching to decipher. In the meantime, I have discovered the following about the school:
the building still exists, though what it is now used for I do not know. It was erected in 1847 as a Board School, and it stands near the Agricultural Hotel. The school itself does not appear to be on Castlegate (unless I have found the wrong school!), but it is on the right hand side of Auction Mart Lane, in a yard that is now used as a glass depot. Auction Mart Lane is not far from Castlegate, but a list of properties now standing in Castlegate does not mention a school. Google Street Level will not take us along Auction Mart Lane (curses! foiled again!), so we cannot get a close look at the old Board School. I'll do some digging re Ernest Robertshaw, but it's dinnertime here, so it might be a few minutes before I can return to the fray.