Primary School, Grade School
You've seen 学校 from a couple levels ago. Now we're adding a small to it. What is a "small school"? That's a school for small people, making it an elementary school.
The reading is the regular on'yomi reading of 小 plus the vocab word 学校 that you've seen previously. Combine these two things for the reading of 小学校.
I am an elementary school teacher.
There are many foreign-born students in the elementary school in this town.
I am in a volunteer club that reads picture books to elementary school children.
I've been interested in you since we were in elementary school.