Hi Bobette,
I do precision teaching with several children, most of them don't have dyslexia but it really works for them as well. As you can see from looking at the link Hollyw gave you it's not restricted to letter work.
One child I work with (yr 1) has trouble recognising simple numbers so we started his probe sheet off with numbers 1-5. He started off only recognising 2 or 3 in a minute and has increased that to 30 in just over two weeks

I also do letters with him and that's greatly improved as well.
I like it because it only takes a couple of minutes each day and the children like it because it's quick and they don't have the chance to get bored

Good luck.
CFB