This reminds me of when we learned about sex and pregnancy at school. Our science teacher told us that if we wanted to have a baby boy, it would be best to do the deed closer or when you ovulate.

If you wanted a girl, you could make love three days before because the girly sperm swims slower.

New Scientist's Bumpology writer sort of reinforces that point, however it had nothing to do with the sperm being faster or slower. Linda Geddes suggests this method as a natural way of selecting your child's gender:

For example, according to the Shettles method, having sex as close to the moment of ovulation as possible is supposed to skew the ratio towards boys: the Y chromosome is smaller, so the reasoning is that Y-carrying sperm swim faster and are first to reach the egg. Meanwhile, shallow penetration is supposed to boost your chances of having a girl, because according to Shettles X-carrying sperm are more robust, and therefore survive longer in the harsh vaginal environment.

Unfortunately, only my science teacher and Shettles believe this theory.

"There's no evidence that male and female sperm swim differently, and there's no evidence that they survive differently," says Allan Pacey, a lecturer in male health at the University of Sheffield, UK.

Geddes goes on to address other methods of conceiving a child with the gender of your choice here.