Dating is a phenomenon that many students first learn about in either middle school or high school. There are many reasons why people date, and most of them have to do with biological responses of attractions. If you are looking for a science fair project then consider science fair projects on dating.
The first issues that you can examine is the body language that is used during a date. You will want to look at how women and men differ in their body language. If possible try to decode this symbolic language to find patterns of attractions. Can you predict if two people are attracted to one another just by watching their body language?
Another issue that you can examine with your science fair project is how biological functions like body temperature and heart rates change when people are attracted to one another. You can utilize a digital thermometer to take body core and surface temperatures of your test partners. To verify if the test subjects are attracted to one another you can have them fill out a questionnaire at the end of each session.
The goal of a science fair project is to find relationships between two variables. In dating science fair projects your variables are going to relate to a specific aspect of dating and some type of biological or psychological response.