Primary School vs. Elementary School

Primary school and elementary school are the same.

The only difference is that (Elementary school) is the preferred term in some countries, particularly those in North America.

(Primary school) is the preferred term in the United Kingdom, India, Ireland, Pakistan, Australia, Latin America, South Africa and New Zealand and in most publications of the United Nations Educational, Scientific, and Cultural Organizations.

Working IN/ON/AT the Computer

a. Dad’s working IN the computer.
b. Dad’s working ON the computer.
c. Dad’s working AT the computer.

Meaning:

a. Dad is fixing the computer.
b. Dad is working over the computer. (It is such a strange location/position for one to work)
c. Dad is working in his computer, maybe writing a financial report or reading an article.