This is from https://pregnancy.about.com/od/genderselection/a/shettlesmethod.htm
What Science Says About Shettles
In talking to families, it is never hard to find women who claim that the Shettles Method worked for them. This anecdotal evidence is, however, not proof of the success of the Shettles Method. There is plenty of scientific study, not conducted by Shettles, that says that the Shettles Method does not work and there is even some scientific evidence that says not only does it not work, but that it can actually prevent you from getting pregnant.
In 1995, the New England Journal of Medicine researchers proclaimed that, "the timing of sexual intercourse in relation to ovulation has no bearing on the sex of the baby. There are also studies found in The International Journal of Fertility and the American Journal of Obstetrics and Gynecology.
Dr. Shettles did numerous studies himself and not surprinsingly they were always positive. Though the majority of scientists have not been able to replicate his supposed success in sex selection. One complaint that many families have about the method is that the guidelines are strict and difficult to follow, particularly the abstinence of sexual intercourse and orgasm at various points.
In the end you have to remember that there are only a few ways to nearly guarantee the sex of your baby and they involve a lot of scientific tinkering with your body and the whole conception process. There is not any easy method of sex selection that can be done at home. Most couples I have interviewed who choose to do at home methods say they went into this with the mindset that they were tipping the scales in their favor in one direction or the other. Some were very disappointed, while others were thrilled.
To learn more about the Shettles Method, please see Dr. Shettles book How to Choose the Sex of Your Baby which gives all of the details on his ideas.