Student or Learner
Dear Mr Answer
what the differences between "on the... side..." and "at the... side...."
'At the side' is used to describe position.
Ex. Trees are planted at the side of the road.
'On the side' is more like an idiom
1. additional. He is a mechanic but he sells cars on the side.
2. secretly. He is married but he has a mistress on the side.
not a teacher