Unless the soil is highly porous, it would not be a good test. Use a good soil-less potting medium, or plain vermiculite. And unless the sand were kept moist, it would also be a poor test of 'faster' growth. The seeds dropped in plain water will rot. Why don't you use sand, potting medium, and vermiculite for the experiment and ditch the water?

You see, seeds (and plants) require oxygen in order to germinate and thrive just as much as they do water and sunlight and CO2. If the soil is mucky and the water stagnant, the seeds just won't do much.

A better 'experiment' might be to take cuttings of the same kind of easy-to-root houseplant (like pothos) for an experiment. 'In which medium will cuttings ROOT faster: potting medium (soilless), sand, or water'?

There is a 1999-2000 science project with this name cached at the link below. Good description and a picture of the student, not the results for some curious reason.

Here is a link that might be useful: Science project