Three different soil particles determine a soils texture. Sand particles are the largest, clay the smallest, and silt is in between. Medium-textured soils (loam, sandy loam, and silt loam) have a good mixture of sand, silt, and clay that is ideal for growing most plants. It is more difficult to grow plants in soils that contain an excessive amount of either clay, sand, or silt.
The easiest way to evaluate your soils texture is to lightly squeeze a handful of moist soil. If the clump crumbles apart, the soil is sandy. If it forms a sticky ball, it is clay. If the soil ends up as a spongy ball, you have loam. Click this link http://www.csgn.org/curriculum-digging.php to go to the California School Garden Network for curriculum activities to evaluate the texture.