... and just to make sure after much searching I have now found the other William Walker on the 1851 census and can you believe his mother is Jean/Jane Adam who actually married a James Barr so this William must have been illegitimate like I thought. I found all this because James his half brother is living with William and his wife Jane/Jean in Dalry. No idea what happen to John Walker his father but it is likely that it was indeed the school teacher that you found Kiterunner.