Left-handers can mirror write more effectively and quickly than right-handers.

Left Handedness

A left-hander is a person who prefers to use his left-hand over his right to perform daily tasks. About 10% of the world's population consists of left-handed persons. Left handedness is a hereditary trait passed down from parents. There is usually more than one left-hander in the family. Left-handers usually have a parent, an uncle or an aunt who is also a left-hander.
Hand dominance may not be directly related to brain dominance. There are opposing views and a lack of substantiated scientific evidence on this.

It is believed by some scientists that left handed and right handed persons are controlled by their different sides of the brain. They believe that a right handed person is controlled by the left side of the brain whereas the left handed person is controlled by the right side of their brain, and that this happens because of the way that the nerves from our brains cross to opposite sides of our body at the neck region. However, hand dominance may not be directly related to brain dominance. There exist opposing views within the scientific community.

Mirror writing

Mirror writing is formed by writing in the opposite direction to what is considered normal writing in a given language. What is written in "mirror writing" is the exact mirror image of normal text. Mirror writing can be read through the reflection of a mirror.

There are usually more left-handed mirror writers than right-handed mirror writers probably because left-handers tend to have "language centers" in both halves of their brain. This causes them to read and write backwards quite comfortably.
 

The hypothesis that left handers will be able to perform mirror writing more quickly than right-handers is correct.

Mirror writing was once used as a form of cipher. In modern times, one of the most common forms of mirror writing is seen on the front of ambulances so that drivers in front of the ambulance can read the text in their rear view mirrors. Famous Italian inventor and painter Leonardo da Vinci was known to have kept most of his notes in mirror language.

Repeat this science fair project by comparing the ability of ambidextrous persons to mirror-write.

Try to conduct another experiment with emphasis on gender and each gender’s ability to perform mirror writing.

Also, does age have any bearing on a person's ability to mirror-write? Are kids better than adults? Are adults better than retirees? How about the level of education of the participant? Does that have a bearing on your results?