With the Whelan Method, you are to have sex four to six days before your temperature rises if you would like to have a baby boy. If you would prefer a girl, wait until two to three days before ovulation to have sex. Whelan based this on a study of 1,300 women charting their temperatures done by Dr. Rodrigo Guerrero.
According to this method and the book giving more details, Boy or Girl?, the success rate for having a girl is 57%. There is a slightly higher success rate for having a baby boy with 65% of the time people conceiving a boy. This method is in direct opposition to the Shettles Method. In fact, there are several pages in Dr. Shettles' book talking about the Whelan Method.
Type and time of insemination within the menstrual cycle and the human sex ratio at birth. Guerrero R. Stud Fam Plann. 1975 Oct;6(10):367-71.
Boy or Girl? Whelan, E. Pocket, 1991.