You know, sewing where half the class want their needle rethreading, DT where everyone needs to use the glue gun and similar occurrences.
It uses the system I first came across as a child in Clarks. You go in the shop, take a ticket with a number on and then wait. In an orderly fashion, those with tickets are seen. The shop assistant decides when they next see someone.
In the classroom, put up five Post-It Notes with the numbers 1-5 on them. If someone needs help from the teacher, they take a number and see what else they can get on with. In order, the teacher calls out which number they will see next (in a "Cashier number 4 please" voice of course!). When the child has been seen, they put their number back for someone else to use. If there are more than one adult in the room, each adult has their own coloured Post-It.
It works quite well. Give it a go.