Answer:

The science fair projects I did in high school were:

1.  Which is which, Coke or Pepsi?

Have several people drink from two cups of soda, with a saltine cracker between.  The study is really about perceptions because both cups have Coke.  Most folks will say the second is Pepsi because the salt on the cracker makes the second one taste sweeter and Pepsi is a sweeter drink.  KEY:  Do the test tasting with only one person at a time.

2.  Handwriting Analysis.

Have several people write a sample text (I used the poem Mary Had A Little Lamb) and sign their name.  Find a book on handwriting analysis (scriptology) and write up a little paragraph about each person from your analysis.  Ask the person and their best friend to comment on the accuracy of your profile.  If you have siblings in the test group (brothers and sisters), compare their handwriting to see if they look similar but have different profiles.

3.  How many licks does it take to get to the Tootsie Roll center of a Tootsie Pop?

Have a lot of people lick one side of a Tootsie Pop and count the licks.  I also tracked if the person had a moist/normal/dry mouth and if they pushed hard/normal.  Average the number of licks.  This is probably enough for the 5th grade level -- ask your teacher for advice.

Then I used linear regression on this data to solve the equation:

Base # of Licks
 - Pushing Hard Effect (0 if normal)
+ Unusually Moist/Dry Mouth Effect (0 if normal)
====================================
= Actual Licks

The math would be too hard for you to do by hand, but you may be able to get someone to help you put the data in a scientific calculator or computer program.

It's been more than 20 years, but I think I found something like:

Base # Licks = 215 licks
Pushing Hard Effect = 75 fewer licks
Unusually Moist/Dry Mouth Effect = 50 more licks

The key is not to get the same answer I got but to show all the steps how to get the answer you got.  By the way, the Tootsie folks are running a Sweepstakes to guess the number of licks -- even if you don't do the experiment (since you're not 13 years old, get your parents to enter the contest).

OFFICIAL How Many Licks Web Page -- http://www.tootsie.com/gal_licks.php
Vintage Tootsie Pop Commercial -- http://www.tootsie.com/gal_commercial.php
Sweepstakes -- http://www.askmrowl.biz/