Single called organism live in a pond behind school

Amoeba

Explanation:

I'm going to guess you're trying to name a single-celled organism that lives in a pond, in this case behind your school. Plenty of ponds contain Protozoa, but if you need a specific one, an amoeba is a good bet. Amoebas like to live in warm, freshwater lakes and rivers, but can essentially be found in any freshwater.