i taught my son to do it using lollysticks-covering the rows that already have the number in them to work out where the number can possibly go (doesn't take long to dispense with the lolly sticks). also work out what numbers are missing from the row and boxes and cross check them eg: if 1,3,5 and 6 are needed to complete the row and one box already contains 1,3 and 5 then 6 is the only no. that can go in that box in that row, elimination is the trick ! writing the numbers needed next to the row or box helps to make it easier too