Mr. Halper's Helpers is the alias of the Talented & Gifted program, which is a group of gifted and talented kids, and it is named as such to avoid kids getting jealous. The group is mentioned in Double Down.
Initially, Greg Heffley thought that the group's function was only to help Mr. Halper with tasks since he was a janitor, though he catches on when he realizes the group members are the smartest kids in class.
When Susan wanted Greg to join the Talented & Gifted program, he had to take a test. He failed, causing Susan to get mad at the school. Later on, their school put him in another group called "Champs", that is used for kids that are having hard times saying the letter "R".