How do I taper a man's haircut in the back along the neckline?

I can give my son a great haircut at home, except for the very bottom along the back. How can I get it tapered next to his neck and not look all blunt and thick there? I have good shears, so that is not the issue.How do I taper a man's haircut in the back along the neckline?
Cut over the comb method. Use shears or clippers.


While you comb up from the bottom starting at a 45 degree angle. By cutting this way, you won't over cut.


Another way is to go and buy some thinning shears and start at the bottom and work your way up. Remember with thinners that you just want to thin it out 1/4 to 1/2 of the length of the strands of hair..How do I taper a man's haircut in the back along the neckline?
The previous answer was very good; the only thing I would add is to use a straight razor or feather razor to taper down and blend. The barbers have been doing it this way for years!