I subbed for the teacher at dd4's school yesterday. The teacher had the worksheets that I was supposed to give to each kid. My dd's was 20 single digit addition problems with two-digit sums. Before I could distribute all the worksheet, dd was done with hers. When I asked how she finished it in literally under 5 minutes, she replied that she has a trick. She picks an easy one first like 5+5, then looks for 5+6, then 5+7 or 6+6 etc. so she doesn't really have to add each time. I thought that was pretty clever. Dd then went on to help the younger kids with their worksheets encouraging them, praising them for their great work and even writing dashed numbers on their sheets so they could trace. Was so much fun to watch her.