Permissibility of the ma'mum delaying following the imam due to a need

As you know, the Zuhr prayer is performed in the schools with the students in congregation. Some of the teachers responsible for organizing the students, preparing them, and arranging them in the rows watch the students after the iqamah, while they are standing in the middle of the rows, until the imam says the takbir for ruku', at which point they bow with him. Is this considered negligence on their part?
There is nothing wrong with this; because their delay until near the ruku' is for a benefit and a need.