Dec. 1, 99 -- Getting kids to eat from all five food groups is a challenge for most parents ... Partly because kids don't quite understand why they need all the different nutrients.

But a hands on study is teaching some Nebraska kids that skipping important food groups can seriously affect their growth.

A test rat and a control rat. Now eight weeks old, litter mates ace and squeeks are nutritionally very different creatures.

For five weeks, fifth graders fed these furry guys a different diet. Ace got food from all five food groups. Squeeks got food from four food groups - all except the dairy group.

Justin Stearns/5th grader: "I just knew calcium would make his bones bigger and stronger and he'd get bigger but I wasn't exactly sure."

Both rats consumed the same amount of calories - to make up for the lack of dairy, squeeks drank sugar water - a close match to a kid favorite - soda pop.

Each week, the kids weighed the rats and charted the results. Students also measured Ace's and Squeek's tails. Each week, the kids charts show Ace outgrows Squeeks.

For teachers, the rat project is a multi-faceted learning tool.

Kris Luxon/fifth grade teacher: "To study the different food groups, for them to be able to see the importance of calcium in the diet, to be able to work with charts and graphs, to be able to gather data and then analyze that data so it's math skills, science skills and reading skills."

After the five weeks, Ace is 57 grams heavier and his tail is one and a half centimeters longer than Squeeks. A difference the kids decide is created by calcium.

These are just the kind of results parents like to hear.

Rats are used because their digestive system is similar to humans. When the experiment was over, the kids got a chance to adopt the rats.